Free online calculators, dev tools & converters for VAT, budgets, distances, right-angle checks, stairs, decking, concrete, brick & block / mortar, mortgages, passwords, QR, JSON, and measurements

Calculator

Good for: shopping totals, simple budgets, scaling measurements, or checking homework—anything that needs several steps in one go. Turn on scientific keys for π, square root, square, and reciprocal on the current value.

How to use (step-by-step):

1. Use the keypad for the row highlighted in the working list (the big green readout mirrors that row).
2. Edit any earlier number or operator in the working list — totals update as you go. You can type directly in those boxes or use the keypad after selecting a row.
3. Need another step? Press + Add another number. Remove a line with Remove.
4. The thin line above the green digits shows the full expression (and the running total when every value is filled).
5. Press = Calculate to confirm and save to History.

Example: shopping trip — first value £12.50, then + £4.99, then + £7.25 → = Calculate gives £24.74. Calculations run left to right (so 2 + 3 × 4 = 20, not 14). Tap Edit in calculator on any History row to bring it back and change a figure.

Unit converter

Good for: DIY and materials (mm ↔ m ↔ ft), cooking weights, luggage ideas, room sizes, temperatures abroad, and quick unit-price comparisons when two packs are sold in different sizes.

How to use: pick a category, type the amount in Convert from, and read every common equivalent below. Convert to puts that unit’s column first; your category and preferred unit are saved on this device. The Pack price & project section can estimate project cost and compare two offers on the same base unit.

Currency converter

Good for: rough trip budgets, comparing an overseas price to home, or ballparking an invoice in another currency—not for exact bank settlement.

How to use: enter the amount, choose From and To currencies, then Convert. Use Refresh rates if the page has been open a long time. Rates are mid-market style from the free ExchangeRate-API (refreshed on their schedule, often about daily). Your card or bank may apply a different rate or fee—check with them before you move money.

Area from common shapes

Good for: turf, carpet, decking, fabric on a rectangular piece, circular patio slabs, or any quote that asks for area in m² or ft² from sizes you can measure.

How to use: choose the shape that matches your job, enter every field it asks for in one length unit (all metres or all feet, for example). The answer and a small diagram update from your inputs — each part of the shape is labelled on the diagram (e.g. Radius (r), Circumference, Base (b), Height (h), sides A/B/C) with your current numbers so you can see where each input belongs. Dashed lines mark perpendicular heights and the small square at the foot shows a right angle. Open Material cost below when you want pack or tile prices from that area.

Volume from common 3D shapes

Good for: storage boxes, skips, tanks, concrete forms, ducts, pipes, fuel drums, sand / gravel piles, silos, propane cylinders, and anything where you need to work out the space inside or the solid volume of a shape you can measure.

How to use: choose the shape that matches your object, then enter every field in one length unit (all metres, all centimetres, or all inches — don’t mix). The answer and a scaled diagram update as you type. The result is in cubic units of whatever unit you entered (metres → m³, inches → in³, etc.). Use the Volume cost tab to price the volume per m³ / ft³, or the Units tab to convert to litres, gallons, etc.

Triangle solver

Good for: site surveys, carpentry cuts, school geometry, or checking a roof or bracket shape when you only know a few measurements.

How to use: under Known, pick the option that matches your tape measure (three sides, two sides plus the angle between them, or angles plus a side). Fill in the boxes in one unit system, then press Solve. You get missing sides, angles, and area where the numbers can form a real triangle.

Circle solver

Good for: round tables, tree trunks, pipe sizes, garden beds, or any disc where you measured one of radius, diameter, circumference, or area.

How to use: type any one of radius, diameter, circumference, or area (leave the others blank). The rest fill in automatically — stick to one real-world unit (e.g. all cm or all m) so the diagram and numbers stay consistent. The diagram below labels each part of the circle so you can see which box matches the measurement you already have: the dashed purple line is the radius (r), the dashed grey line across the middle is the diameter (d), the dashed blue arc around the rim is the circumference (C), and the filled disc is the area (A). Values on the diagram update as you type.

Use consistent units (e.g. all metres). π used internally with double precision.

Custom closed outline (e.g. room)

Good for: L-shaped or odd rooms, quick site sketches, and “how much floor / skirting” when a simple rectangle is not enough. Decide what one drawing unit means in the real world (often 1 unit = 1 metre on plan).

Draw: click to place corners — a dashed preview follows your cursor from the last corner so the next wall lines up before you click. After three or more corners, move near the green start to snap closed (the ring grows when you are close enough). Closing wins over dragging that corner if both would match. Pan: drag empty space (cursor grab). Zoom: mouse wheel on the drawing. Fit view frames the whole outline. Wall line sets outline thickness on screen; Label size scales length/angle boxes so they do not swamp the plan when zoomed out. Split an edge: turn Add point on edge on, move along a wall until the cursor shows copy, then click; or double-click a wall when the shape is closed. Drag corners to adjust. Shift while placing a new point disables angle snap (same as the preview when held). Edit length boxes on each edge (Enter or blur to apply). When closed, ∠ boxes set interior angles (yellow = locked).

Doodle pad — free in-browser sketch pad

Good for: quick doodles, rough floor plans, wireframes, flow diagrams, kids' drawings, or any sketch you want to save as a PNG — all in your browser with nothing uploaded to our servers.

How to use: pick a tool (pencil, eraser, spray, line, rectangle, circle or fill), choose a colour and thickness, then draw on the canvas. Undo steps back up to 100 actions, Snap locks line / shape tools to corners you've already drawn, and Save PNG downloads your drawing. Your current sheet auto-saves in this browser so you can come back to it later.

VAT / sales tax (add-on %)

Good for: quick checks on quotes and receipts—turning a net price into gross (with tax) or stripping tax off a total to see the net. Default 20% matches common UK VAT; change the rate for other countries or reduced rates.

How to use: set the Rate (%), then enter either Net amount or Gross amount (leave the other empty). The tool fills in tax and the missing total. Illustrative only—real rules can depend on what you sell and where; use an accountant for compliance.

Margin & markup

Good for: retail and trade pricing—seeing whether a sell price covers stock cost, or working backwards from a target margin on sell (what many accountants mean by “margin”).

How to use: enter Cost and Sell price to see profit, margin %, and markup %. Optionally add Target margin % on sell with cost filled in to get a suggested sell price. Margin % is profit ÷ sell; markup % is profit ÷ cost—they are not the same number at the same price.

Loan payment (amortising)

Good for: ballparking car loans, personal loans, or hire-purchase style deals with a fixed APR and the same payment every month until paid off, plus checking how much a lender payment would be relative to income.

How to use: choose Mode. Payment estimate uses loan amount, APR, and term. Affordability uses income, a maximum share of income for payments, APR, and term to estimate the largest loan that fits that limit. Illustration only—lenders add fees, stress tests, and credit checks.

Estimated regular monthly payment: 195.66 · Total repaid across the term: 11,739.69 · Total interest: 1,739.69 · That would use about 6.1% of your monthly income

Mortgage calculator

Good for: estimating monthly mortgage costs before a house purchase, comparing deposit sizes, stress-testing rates, or seeing how overpayments change payoff time.

How to use: enter the home price, choose whether the deposit is a cash amount or a percentage, then add the interest rate and term. Optional yearly tax, yearly insurance, monthly HOA / service charge, and monthly overpayment help you ballpark a fuller housing cost. If a cost does not apply, leave it as 0.

Budget calculator

Good for: a single-adult, couple, family, lone-parent, retired, student, shared household or carer budget — covering income, housing, bills, food, transport, healthcare, childcare, pets, debt, savings, lifestyle and more, with optional line-by-line breakdowns.

How to use: pick a mode, add your household details, then fill each section’s top total or tap “Show detailed breakdown” to split it into line items (which auto-sum into that total). All amounts are for one month. Nothing you type leaves your browser unless you press Save or Export. This is a planning aid, not regulated financial advice.

Total planned monthly spending: 2,770.00 · Money left after listed spending: 430.00 · Planned savings rate: 9.4% of income · Essential costs: 2,070.00 (64.7% of income) · Flexible spending: 400.00 (12.5% of income)

Distance calculator & route planner

Good for: measuring straight-line distance or real travel distance along a route with as many stops as you like — driving sticks to roads, while walking and cycling also follow public footpaths, bridleways, tracks, and cycle paths wherever OpenStreetMap knows about them.

How to use: click anywhere on the map to drop a numbered pin. Each new click adds the next stop in order — the first pin is your start, the last is your finish. Use the list below the map to rename the order (type a new number, or use Up / Down), remove a stop, or drag a pin to fine-tune it. Need to insert a point inside an existing route? Click Add point between…, pick which two stops to insert between, then click the map.

This tool uses your browser plus free, open map & routing services directly — tiles from OpenStreetMap, driving routes from OSRM, and walking/cycling routes from BRouter (which can follow public footpaths, bridleways, cycle paths, and tracks tagged in OpenStreetMap). Routing depends on third-party availability; if a service is offline we fall back to direct distance and tell you.

Spotty or no mobile data: areas you have already panned or zoomed on this device are saved automatically in your browser, so the map can still show there while offline. When you start navigation we automatically pre-pan around the planned route to warm nearby map tiles for your current zoom. Your GPS location still updates without data. New route calculations, search, community POIs, and off-route recalculation usually need the internet.

Right-angle diagonal check

Good for: checking whether two adjoining sides can be set out square, working out the diagonal for a 90-degree corner, and scaling 3-4-5 style layout checks in whatever unit you prefer.

How to use: enter the two side lengths that meet at the corner, choose your unit, and the tool will calculate the diagonal that should measure between the endpoints if the corner is truly 90 degrees.

Tip & split bill

Good for: restaurant bills, service charges, takeaway collections, and any shared spend where you want a fair total per person.

How to use: choose an equal split or itemized split. Itemized mode lets each person pay their own subtotal, then adds tip and service on top of what they personally owe.

Compound interest

Good for: savings growth estimates, investment illustrations, and seeing how regular monthly contributions can build over time.

How to use: enter the starting amount, interest rate, years, compounding frequency, and any regular monthly contribution. The tool shows the final value and a year-by-year breakdown.

Year | End balance | Interest earned
1 | 6,483.70 | 283.70
2 | 8,043.30 | 359.60
3 | 9,682.69 | 439.40
4 | 11,405.97 | 523.27
5 | 13,217.40 | 611.44
6 | 15,121.51 | 704.11
7 | 17,123.05 | 801.53
8 | 19,226.98 | 903.93
9 | 21,438.55 | 1,011.57
10 | 23,763.28 | 1,124.72

Wall area calculator

Good for: paint prep, wallpaper estimating, plastering quotes, and checking net wall area after doors and windows are deducted.

How to use: enter room length, room width, and wall height in metres, then the total number and sizes of doors and windows to subtract from the gross wall area.

Wallpaper roll calculator

Good for: estimating wallpaper rolls before you buy, allowing for openings, and padding the result for trimming and pattern matching.

How to use: enter the net wall area or the room size via the wall area tool, then add roll width, roll length, and a wastage allowance. A pattern repeat allowance can be entered as an extra % if needed.

Stair calculator

Good for: rough stair planning, checking rise per step, estimating total run (going), and seeing whether a stair feels too steep before you build it. Defaults follow UK Building Regulations Approved Document K for private / domestic stairs.

How to use: enter total rise, your preferred maximum rise per step, and the tread depth (going) you want. Keep Enforce UK building regs ticked for private domestic stairs. Untick it for loft conversions, commercial stairs, or if you know you’re working to a different standard. A live diagram updates as you type.

Fence job calculator

Good for: timber panel fences, closeboard / feather-edge, picket, post-and-rail / arris, and chain link. Works out bay count, post count (line, corner and end), spacing between posts, run-by-run breakdown across corners, and a materials list with pricing per item.

How to use: pick the fence type, enter the total run, choose Unit (m, ft, cm, mm, in, or a custom label) for every length on this tool, then set spacing and height in that unit. For timber panel fences, choose the panel post system (centre-to-centre, face-to-face + post thickness, or slotted timber / concrete with slot allowances). Corners split the fence into straight sections — each is pre-filled with an equal share of the total. Open Advanced: materials & pricing for a full take-off.

Decking material estimator

Good for: quick deck take-offs, board counts, joist-line estimates, fixings and screw boxes, deck oil / paint / varnish cans, and total material cost — all from deck size, board width, gap, stock length, joist centres, and the prices you pay.

How to use: enter deck length and width, board face width, board gap, stock board length, joist centres, and a wastage allowance. Keep all length inputs in the same unit — the tool auto-suggests metric or imperial based on your region, and you can switch any time. Open the Pricing, Joist details, Fixings, or Treatment (oil / paint / varnish) panels only when you need them; prices use the Prices in currency at the top of the page.

Concrete volume, mix & cost calculator

Good for: slabs, strip footings, shed bases, pads, and post holes — plus working out the cement, sand, aggregate, water, fibres, bag counts, and total cost for common UK mix grades (C10 to C40) or your own custom ratio.

How to use: pick a shape and enter dimensions to get the wet volume (all dimensions in one calculation must use the same unit). Then open Mix design, Bags & weights, or Pricing only if you need them — the tool stays simple until you toggle each section on.

Brick, block & mortar calculator

Good for: boundary walls, garden walls, garage walls, extensions, and cavity walls — quickly working out how many bricks, blocks, cement bags, and how much sand you need, plus a total material cost in your own currency.

How to use: pick a wall type (single-skin brick, single-skin block, or cavity wall), tell the tool the wall size either as a total area or as a length × height, and (optionally) deduct door / window openings. Then open Mortar mix or Pricing panels only if you need quantities and costs — the tool stays simple until you toggle each section on. Every input in one calculation must share the same unit.

Recipe scaling tool

Good for: increasing or reducing recipes, batch cooking, meal prep, scaling portions for catering, and working out how many packs, bottles or tins you need to buy along with the total cost (including wastage) for the quantity of portions you are making.

How to use: set your original and desired servings, then add each ingredient below — name, type, unit and amount, then Add. Open Pack size & pricing on an ingredient to unlock pack-count, itemised costing, wastage and totals in the result panel, along with pie-chart breakdowns of cost and wastage.

Keyword generator

Good for: developers, site owners, freelancers, agencies, and content teams trying to generate search-friendly keyword ideas from a page topic, audience, and benefit.

How to use: describe the page topic, who it is for, and the main benefit. The tool combines your inputs with browser-side phrase building and optional public word suggestions, then ranks the results by fit and search intent.

Password generator

Good for: quickly creating strong passwords for websites, apps, databases, admin panels, and internal tools without sending them to your server.

How to use: choose a length, pick the character sets you want, optionally exclude similar-looking characters, then generate and copy the password. Everything runs in the browser.

QR code generator

Good for: website links, contact pages, event posters, Wi-Fi sharing, menus, and quick mobile handoff from screen to phone.

How to use: choose the content type, enter the value, then generate a QR code in your browser and download it as an image.

JSON formatter & validator

Good for: developers, API debugging, config files, quick payload cleanup, and checking whether copied JSON is valid before using it.

How to use: paste JSON, then validate, pretty-print, or minify it in your browser. Invalid JSON shows a clear error instead of silently failing.

Date & time difference

Good for: notice periods, rental gaps, project timelines, warranty “30 days from purchase,” precise age (down to the second), contract durations billed to the minute, uptime / downtime windows, “how long until the deadline,” or “what date-time is 90 working hours after kick-off?”

How to use: pick a start and end date. Leave the time boxes blank (or at 00:00) if you don’t care about times, or type them in for second-level precision. You’ll see a calendar breakdown (years, months, days, hours, minutes, seconds — correctly handling leap years and different month lengths), plus the running total expressed in each unit. Tick or untick the unit toggles to show only the ones you want. Below that, you can add any amount of years / months / weeks / days / hours / minutes / seconds to the start to get the resulting date-time.

Add time to the start date

Calendar-aware: adding months or years lands on the correct day of the target month (Feb 29 + 1 year rolls to Feb 28 in a non-leap year). Use a negative number to go backwards.

World time zones

Good for: scheduling calls with clients or family abroad, checking “is it still office hours there?”, or lining up a release time with another country.

How to use: type a city or region in Add region, pick from the list, then Add. Your device clock drives “now”; standard IANA zones (e.g. Europe/London) handle daylight saving correctly. Remove last drops the last row; Reset defaults restores a starter set. Your list is saved in this browser. Times tick every second while this tab is open.

Fuel trip cost

Good for: “roughly what will this drive cost?” before a long trip, or comparing two cars using their consumption figures. Pick the currency and pump unit for your country (UK: £ per litre; US: $ per US gallon; EU: € per litre, and so on).

How to use: choose a Preset (or Custom) and the tool sets sensible currency, distance, consumption and volume units for you. You can always override each dropdown. The estimate updates live — traffic and driving style will change real use.

Percent helpers

Good for: exam-style “what percent is this of that?”, sale prices after a discount %, reporting growth between two numbers, and reverse-percentage checks where you know the final value and the rate.

How to use: pick a Mode. Reverse modes help when you know the discounted or increased result and need to work back to the original number.

A is 12.5% of B.

Average (mean)

Good for: class grades, repeated measurements, sample costs, or any set of numbers where you want the usual “add them up and divide by how many” average.

How to use: type each value on its own row. Add value adds another row (as many as you need, up to the limit). Remove deletes a row if you typed one twice or do not need it. Blank rows are ignored when you press Calculate average so you can leave spare lines empty.

Average: —

Paint quantity (tins)

Good for: decorating one room when the tin says “covers X m² per litre” and you know how many coats you want—so you do not buy three tins when one would do (or the opposite).

How to use: either tick Use area directly and type wall/ceiling area in m², or leave it off and enter width × length for a simple rectangular painted surface. You can also subtract doors, windows, or other unpainted openings as one total area. Add coats, the can’s coverage (m² per litre), and tin size (L). The answer rounds up to whole tins.

Net painted area after deductions ≈ 20 m² · Paint volume needed ≈ 3.33 L · Tins (5 L each): 1 (rounded up)

Roof pitch & slope

Good for: matching an existing roof pitch, briefing a builder (“6 in 12”), or converting between ratio, degrees, and percent grade (useful for ramps and drives too).

How to use: enter rise and run in the same units (e.g. both inches, or both cm)—the ratio is what matters, e.g. 6 : 12. Read off angle and grade; tweak rise or run to see how steep the slope becomes.

Invoice line (ex-tax + tax)

Good for: freelancers and small shops checking a single invoice line—quantity × unit price, optional line discount %, then VAT/sales tax on the discounted line (common UK-style “ex-VAT” wording).

How to use: all prices are excluding tax until the last step. Enter quantity, unit price (ex tax), any discount % for that line, and the tax rate %. Read line subtotal, tax, and line total including tax.

Cutting list (sheet / board)

Good for: estimating how many stock boards to buy, rough wastage, and material cost per part for sheet goods (plywood, MDF, laminate, acrylic) when parts are cut on a rectangular grid with kerf between cuts.

How to use: enter a job name and one row per component. Use the same length unit everywhere (for example millimetres). 1st / 2nd cut sizes describe machining steps; the tool uses the larger length and width (blank size) to fit on stock. Edge trim is subtracted once from stock length and once from stock width (total squaring loss). Kerf is applied between adjacent parts on the sheet. Rows that share the same material and stock settings are grouped: you will see if identical blanks could use fewer boards, and an area-based lower bound for mixed sizes.

Tip: hover any column heading or input for a short explanation. Open Field guide below for the full list.

Sleep cycle calculator

Good for: working out a bedtime that lines up with full sleep cycles so you wake feeling less groggy, or deciding when to set the alarm if you are going to bed now. Also handy for naps, shift work, jet-lag planning, and kids’ routines.

How to use: pick a mode — I want to wake up at… shows six suggested bedtimes; I’m going to bed at… shows six suggested wake times; Go to bed now uses your device’s current time. Adjust the time to fall asleep buffer (how long you usually take to drift off) and the cycle length (90 minutes is the common average). Results pick cycle counts that typically cover a full night; earlier times mean less sleep, later ones mean more.

What is my IP address?

Good for: router and port-forward setup, remote access, whitelisting an address with a supplier, support tickets (“please confirm your public IP”), checking whether a VPN or proxy is active, and telling IPv4 from IPv6.

How to use: open this tool and your public IP address loads automatically. Click Refresh if you change network or toggle your VPN. The approximate location comes from an IP-to-location lookup — it’s based on your ISP’s allocation, not GPS, so a nearby city or region is normal. Private/local addresses (e.g. 192.168.x.x) are not shown here — those only exist inside your home or office network.

Volume & cost per unit

Good for: pricing timber (e.g. a 2.4 m × 45 mm × 95 mm rail for £X), concrete, topsoil, bark, compost, aggregates, foam, stone, water tanks, storage boxes, or anything sold by volume. Enter the shape and price in any unit system and the tool gives you the volume plus the price per m³, cm³, litre, in³, ft³ and yd³ so you can compare suppliers across units.

How to use: pick a shape, choose the dimension unit all measurements are in, and fill in the sizes. Optionally enter a quantity (number of pieces) and a price — choose whether that price is per piece or for the whole lot. The currency follows the selector near the top of the page. Results update live.

Currency follows the selector at the top of the page. Leave the price blank to see volume only.