Unit Converter

Convert length, weight, temperature, area and volume units

How it works

Unit Converter — Convert length, weight, temperature, area and volume units. All processing happens in your browser — no upload, no signup, no email required. Free forever.

Last updated: 2026-05-06

Editor's note

We hated the silent bug we kept seeing in other converters: switch the category from length to weight and the previous unit selection lingers in a half-broken state, so "5 feet" silently becomes "5 kilograms" the moment you change category. We saw three popular tools do this. Our category switcher resets the From and To units on purpose, because mixing imperial inputs with a metric label is the single most common silent error in unit math, and one extra reset click beats a wrong answer that looks plausible.

The other design call we kept relitigating: how many digits to show. Show too few and a 0.0254 conversion factor rounds into the noise; show too many and the user copies an absurd false-precision figure into a contract. We landed on 8 significant digits with scientific notation kicking in only at extremes. It is the smallest number we could defend for woodworking measurements, recipe scaling, and freight calculations alike — boring on purpose.

About Unit Converter

The unit converter is a single, fast tool for switching between every measurement system you actually use day to day. Whether you are translating a recipe from cups to milliliters, sizing a parcel that is listed in pounds for a courier that prices in kilograms, or converting an oven temperature from a US recipe so it makes sense in your fan-forced electric oven, the conversion happens instantly as you type — no spreadsheet, no second tab, no risk of an off-by-1000 mistake from confusing grams with kilograms.

Pick a category (length, weight, temperature, area, volume, time, or speed), choose the source and target units from the dropdowns, type a number into either input, and the other side updates in real time. Conversions use the standard internationally-defined ratios: 1 inch is exactly 0.0254 m, 1 lb is 0.45359237 kg, 1 mile is 1.609344 km. We display 8 significant digits and switch to scientific notation only for extreme magnitudes so the answer you copy back into your work is precise enough for any practical purpose.

Worked example: 5 kilometers equals 5 / 1.609344 = 3.10686 miles, and 100 °F equals (100 − 32) × 5 / 9 = 37.778 °C. Because each unit is defined relative to a base unit (meter, kilogram, kelvin, etc.) the conversion is symmetric — swap the source and target and the result simply runs through the inverse function.

How to use Unit Converter

Choose a category from the Category selector at the top (Length, Weight, Temperature, Area, Volume, Time, Speed).
Pick the From unit on the left side dropdown.
Pick the To unit on the right side dropdown.
Type a value into either input — the opposite side recalculates instantly.
Use the swap arrow in the middle to flip From and To if you typed into the wrong field.
Copy the result by selecting it; nothing leaves your browser, so you can paste sensitive numbers freely.

Common use cases

Translating a US recipe into metric for a European kitchen — cups to milliliters, ounces to grams, °F to °C.
Sizing a shipment for a courier whose pricing breaks at 5 kg, 10 kg, 20 kg when your scale reads pounds.
Converting CAD drawing dimensions between millimeters and inches when collaborating with a US fabricator.
Estimating jogging pace by switching between km/h, mph, and min/km equivalents.
Reading scientific papers that mix hectares, square meters, and acres for the same plot of land.

Tips & common mistakes

Temperature is not a ratio — multiplying °C by a constant does not give °F. Always run the value through the converter rather than scaling it manually.
Watch the prefix on weights: 'mg' (milligram) is one millionth of a kilogram, while 't' (metric tonne) is one thousand. A typo of one character changes the answer by a factor of a billion.
For volume, 'cup' here is the US legal cup of 240 ml. UK and metric cups differ — pick the recipe's locale before converting baking volumes.
Speed in 'knots' is nautical miles per hour, not statute miles. Use it for sailing or aviation, not road driving.

Frequently asked questions

Which units are supported?

We cover length (mm/cm/m/km/in/ft/yd/mi), weight (mg/g/kg/t/oz/lb), temperature (°C/°F/K), area (mm²–km², ha, ac, ft²), volume (ml, L, m³, tsp, tbsp, cup, gallons), time (ms→weeks) and speed (m/s, km/h, mph, knots).

Are conversions exact?

Conversions use the standard internationally-accepted ratios (e.g. 1 inch = 0.0254 m exactly). We display 8 significant digits and switch to scientific notation for extreme magnitudes.

Why does swapping the units flip the result?

Each unit has a 'to base' and 'from base' function. Swapping just runs the inverse conversion — the underlying value never changes.

Can I convert between categories — for example liters to kilograms?

No. Liters measure volume and kilograms measure mass; the relationship depends on the substance's density (1 L of water is 1 kg, but 1 L of olive oil is 0.91 kg). Look up the density first and multiply manually, then convert within a single category.

Why do I sometimes see scientific notation like 1.234e-7?

When the result has more than 8 leading zeros or is larger than 100 million, fixed-point notation becomes unreadable. We switch to exponential form so you can still see the significant digits at a glance.

Does the converter remember my last category?

It resets to Length on each page load to keep the URL stateless. If you frequently use a specific category, bookmark the page after picking it — your selection persists for that browser session.