Calculators
All Stable Numbers calculators and explainers in one place.
Age Calculator
Work out your exact age in years, months and days. See total days lived, next birthday and day of the week. Supports a custom target date.
Open tool →Area Calculator
Calculate the area (and perimeter) for common shapes including rectangle, square, circle, triangle, trapezoid and ellipse. Supports unit labels, precision control, share link and CSV export.
Open tool →BMI Calculator
Free BMI calculator with metric and imperial units. Enter your height and weight to see your Body Mass Index and category instantly.
Open tool →Carbon Footprint & Tree Offset Calculator
Calculate your carbon footprint and understand tree planting offsets. Interactive tool covering transport, home energy, diet and lifestyle. See how many trees would offset your emissions with realistic timelines.
Open tool →Date Difference Calculator
Calculate the precise difference between two dates with optional time, business-day counting, weekend exclusion, custom holidays, and add/subtract duration mode. Share your setup and export CSV.
Open tool →Online Ruler (mm, cm, inches)
True-to-size online ruler in millimetres, centimetres and inches. Calibrate by screen size or match a credit card. Horizontal and vertical rulers with crisp tick marks. Share your calibration.
Open tool →Paint Calculator
Work out how much paint you need for a room. Enter room dimensions, doors and windows, number of coats, coverage per litre and wastage. See litres required and tins by size. Share link and CSV export.
Open tool →Pythagoras Calculator
Solve right-triangle sides with the Pythagorean theorem. Find the hypotenuse or a missing leg, see worked steps, angles, area and perimeter. Unit label, precision, share link and CSV export.
Open tool →Recipe Servings Scaler
Scale any recipe up or down. Paste ingredients, set original and target servings, choose rounding and fraction style. Instant scaled list, share link and CSV export.
Open tool →Scientific Calculator (Accessible)
A privacy-first scientific calculator with large, high-contrast buttons. Trig, logs, powers, roots, factorial, memory keys, degree/radian toggle and full keyboard support. Distraction-free popup mode.
Open tool →Tile Calculator
Work out how many tiles you need for a floor or wall. Enter room or wall size, tile size, optional grout gap, wastage and tiles per box. See tiles required, rounded tiles and boxes. Share link and CSV export.
Open tool →Unit Converter
Fast unit converter for length, mass, temperature, volume, area, speed, time and data. Instant two-way conversion, precision control, swap inputs, share link and CSV export.
Open tool →Volume Calculator
Calculate volumes for common 3D shapes including cube, cuboid, cylinder, sphere, cone, pyramid and ellipsoid. Unit labels, precision control, share link and CSV export.
Open tool →Wallpaper Calculator
Estimate how many wallpaper rolls you need. Enter wall run or room size, roll width and length, pattern repeat and match type, trim allowance and optional openings. Share link and CSV export.
Open tool →Work with numbers without the faff
This hub brings all Stable Numbers calculators into one tidy place. Each tool is built for speed, clarity and accuracy, so you can go from input to answer in seconds. If you need the method, every page includes a short explainer and a worked example in plain English. No fluff. No distractions. Just the steps that matter.
You will find everyday essentials such as percentage increase and decrease, VAT, profit margin and markup, gross to net and common unit conversions. More tools will be added over time based on what people use most and what is most requested. The layout stays clean across devices, with labels that make sense and results that are easy to copy.
Bookmark this page if you work with prices, quotes, discounts or growth figures. It is designed to save time, reduce errors and help you sense-check claims without opening a spreadsheet. If there is a calculator you would like to see, send a request and it will be prioritised by demand. Stable Numbers is a practical resource first, here to make number work simple.