Unit Converter — metric and imperial

Pick a category, type a value, and read the converted result instantly. Seven categories covering everyday and engineering units, all running in your browser.

Why this converter?

A unit converter is one of those tools you reach for ten times a year for forty seconds. Cooking from a US recipe in a French kitchen, sizing a part on a metric drawing while shopping in inches, sanity-checking a fuel-economy figure across hemispheres — all easier when the conversion happens instantly without firing up a calculator app.

This tool keeps the unit list opinionated: the units people actually search for, with conversion factors based on the SI standard or the most widely accepted definition. For temperature it handles the affine offset (°F is not a linear scale of K) properly; for everything else it's a simple multiply-and-divide chain through SI base units.

How to use this tool

Pick a category at the top: length, weight, area, volume, speed, time or temperature.
Type a value on the left and pick its unit from the dropdown. The result is computed live for the unit on the right.
Use Swap to flip the input and output units when you need the inverse direction. Change either dropdown at any time — the result stays in sync.

Frequently asked questions

Which conversion factors are used?

Length, weight, area and volume use the SI-derived definitions: 1 inch = 0.0254 m exactly, 1 pound = 0.45359237 kg exactly, etc. Speed and time use the same chain through seconds. Temperature handles the °F-°C affine relationship and absolute zero correctly.

Why is volume split into US and UK gallons?

They are different units. 1 US gallon is 3.785 L; 1 UK (imperial) gallon is 4.546 L — about 20% larger. Mixing them up in cooking or fuel-economy calculations is a classic source of errors. The labels make the choice explicit.

What's the difference between m³ and L?

1 m³ = 1000 L exactly. The cubic-metre is the SI base for volume; the litre is the everyday unit. The tool exposes both so you can pivot between engineering specs and recipes without juggling factors.

Why does temperature behave differently?

Length and weight conversions are linear (multiply by a factor). Temperature has an offset: 0 °C ≠ 0 °F. The tool routes everything through Kelvin internally to handle the offset cleanly, then converts back to the target scale.

Are conversions exact or rounded?

The factors used are exact when the international agreement defines them exactly (e.g. 1 inch = 25.4 mm exactly since 1959). The displayed result is rounded to ~8 significant digits so it fits readably; for engineering precision, copy the value into a tool that handles arbitrary precision.

Common use cases

Where flipping a quick conversion saves real seconds.

Cooking from foreign recipes

Convert 2 cups → mL, 1 lb → kg, 350 °F → °C in seconds. The tool handles the US/UK gallon difference so 'gallon' isn't ambiguous in your conversion.

DIY and home improvement

Need 8 ft of timber but your tape is metric? Type 8, pick ft → m. Read the result, mark the cut, save yourself a wrong-length trip back to the shop.

Engineering spec checks

Comparing two component datasheets in different unit systems? Convert weight, area or volume figures into matching units before plotting.

Travel planning

How fast is 80 mph in km/h? How many km in 200 mi? The speed and length categories give answers without leaving the page or pulling up Google.

Tips and shortcuts

Habits that prevent unit-conversion bugs.

Always state the unit when sharing numbers

'30' alone is meaningless. '30 km' or '30 mi' is unambiguous. Whether you're texting a colleague or filing a bug, including the unit prevents the most common factor-of-1.6 mistake.

Beware US vs UK gallons

Recipes from the UK use imperial gallons (~4.55 L), recipes from the US use US gallons (~3.79 L). When in doubt, prefer mL or L — they mean the same thing everywhere.

Round at the end, not in the middle

Chaining multiple conversions and rounding at each step accumulates error. Keep full precision until the final display, then round once.

Volume is not weight

1 cup of flour is not 1 cup of water by weight (~120 g vs 240 g). Volume-based recipes are forgiving for liquids but wrong for dense solids — convert to grams when accuracy matters.