Free Online Unit Converters

Why Use Free Online Unit Converters?

Unit conversion is one of the most common everyday calculations, yet most people either search for a specific conversion each time or try to remember formulas. A dedicated converter tool shows every related unit at once, so you can compare values side by side instead of making multiple searches. These converters update all units live as you type in any field — no "Convert" button needed.

Length and Distance

The Length Converter supports 16 units from millimetres to nautical miles, including the metric system (mm, cm, m, km), imperial system (inches, feet, yards, miles), and specialised units like light-years and astronomical units. A dedicated height conversion section converts between feet/inches and centimetres — the most common length conversion people search for. Popular sub-routes like cm-to-inches and feet-to-metres give you instant access to the most frequent conversions.

Weight and Mass

The Weight Converter handles 13 units including grams, kilograms, pounds, ounces, stone, metric tonnes, and more. A body weight section displays stone + pounds format used in the UK alongside kilograms and pounds for easy comparison. Whether you're converting cooking measurements, shipping weights, or body weight between systems, every unit updates live.

Temperature

Temperature conversion uses non-linear formulas unlike most unit conversions, which makes it harder to do mentally. The Temperature Converter handles Celsius, Fahrenheit, Kelvin, and Rankine with a visual thermometer and a reference table showing common temperatures (boiling point, body temperature, room temperature, freezing point) in all four scales. Absolute zero validation prevents impossible negative Kelvin or Rankine values.

Speed and Data Storage

The Speed Converter covers 9 units from metres per second to Mach numbers and even furlongs per fortnight. A context panel shows real-world speed references so you can visualise what a given speed actually means. The Data Storage Converter handles both SI decimal (KB, MB, GB) and IEC binary (KiB, MiB, GiB) standards, includes a "why does my drive show less" explainer, and a hard drive calculator that shows the difference between advertised and actual capacity.

Area

The Area Converter supports 14 units including square metres, square feet, acres, hectares, square kilometres, square miles, and more. It's particularly useful for property sizes — quickly compare listings in acres vs hectares, or convert square footage to square metres when comparing international real estate. All units update live as you type in any field.

Volume

The Volume Converter handles 18 units across metric (litres, millilitres, cubic metres), US customary (US gallons, US fluid ounces, US cups), and UK imperial (imperial gallons, imperial pints) systems. A built-in cooking reference section shows common recipe conversions. The distinction between US and UK volume units is clearly labelled to prevent the confusion that causes many cooking and mixing errors.

Currency

The Currency Converter supports 30+ currencies with exchange rates sourced from the European Central Bank, updated daily. Convert between major currencies like USD, EUR, GBP, JPY, and AUD, as well as many others. Unlike most currency converters, this tool runs client-side after fetching the latest rates — your conversion amounts are never sent to a server.

Angle

The Angle Converter handles degrees, radians, gradians, arcminutes, arcseconds, turns, and milliradians. A visual angle display shows the current angle on a protractor-style graphic, and a common angles reference table lists frequently used values (30°, 45°, 60°, 90°, 180°, 360°) in all supported units. Particularly useful for engineers, students, and anyone working with trigonometry or navigation.

Fuel Efficiency

Fuel efficiency is uniquely tricky because MPG and litres per 100 km have an inverse relationship — doubling MPG does not halve L/100km proportionally. The Fuel Efficiency Converter handles MPG (US), MPG (UK/Imperial), litres per 100 km, and kilometres per litre, correctly managing the US vs UK gallon difference. Essential for comparing vehicle specifications across American, British, and European markets.

Pressure

The Pressure Converter supports PSI, bar, pascal, kilopascal, atmospheres, millimetres of mercury (mmHg), torr, and inches of mercury. A tyre pressure section provides quick conversions between PSI and bar — the two most common tyre pressure units worldwide. Also useful for weather (atmospheric pressure), medical (blood pressure in mmHg), and engineering applications.

Energy

The Energy Converter handles joules, kilojoules, calories, kilocalories (food calories), kilowatt-hours, BTU, electronvolts, and foot-pounds. It clearly distinguishes between the physics calorie (cal) and the food Calorie (kcal) — a common source of confusion. Use it to compare energy bills (kWh), nutritional labels (kcal), heating values (BTU), and physics calculations (joules) in a single view.

Number Base

The Number Base Converter converts between binary (base 2), octal (base 8), decimal (base 10), and hexadecimal (base 16), with support for custom bases from 2 to 36. Bitwise operations (AND, OR, XOR, NOT, shift) are included for developers and computer science students. Useful for debugging, colour codes (hex), file permissions (octal), and understanding how computers represent data.

Shoe Size

Shoe sizing systems vary wildly between countries and have no simple mathematical relationship. The Shoe Size Converter maps between UK, US, EU (Continental), Japanese (cm), and Mondopoint sizing for men's, women's, and children's shoes. Essential when shopping from international retailers — a US 10 is a UK 9 and an EU 43, but only if it's men's sizing.

Clothing Size

The Clothing Size Converter handles UK, US, EU, Italian, French, Japanese, and Australian sizing for tops, bottoms, and dresses. A body measurement guide helps you find your correct size when you know your chest, waist, or hip measurements in either centimetres or inches. Particularly useful for online shopping from international brands where size labels differ significantly.

Privacy: Everything Runs Locally

All conversions happen entirely in your browser using JavaScript math. No data is sent to a server, no values are logged, and nothing is stored. The tools load instantly, work offline once cached, and have no rate limits or account requirements. The only exception is the Currency Converter, which fetches daily exchange rates from the ECB — but your conversion amounts stay local.