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Calculators · Updated October 20, 2026

Unit Converter — Length, Mass, Temperature, Volume, Speed

You can convert between metric and imperial units of length, mass, temperature, volume and speed as you type, and see the same value listed in every unit in the family.

Runs in your browserFree · No sign-up · No watermark
UnitsRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
Units
Processing
In your browser
Price
Free, no account
Updated
October 20, 2026
All Calculators

About Unit Converter

Unit conversion is a small task with a large failure rate: a recipe in cups and a scale in grams, a run measured in miles per hour, a spec sheet in millimeters and a tape measure in inches. Most mistakes come from multiplying by the wrong factor or losing track of which unit is the source. This converter keeps both units visible and updates the answer as you type.

Five families are covered: length, mass, temperature, volume and speed. Temperature gets its own treatment because the scales use offsets as well as factors, so the tool shows the formula that actually ran. Below the result, every unit in the family is listed with the same value, which makes the conversion easy to check and easy to copy into whatever unit a form expects.

What this tool does

The details that matter when you use Unit Converter for real work.

  • Five unit families

    Length from millimeters to miles, mass from milligrams to pounds, Celsius, Fahrenheit and Kelvin, US volume units, and speed including knots.

  • Live conversion with swap

    The answer updates as you type, and Swap units reverses the direction while turning the current answer into the new input.

  • All equivalents in one table

    Every unit in the family is listed with the same value, so the answer can be read in the unit a form or recipe expects before copying.

  • Temperature handled correctly

    Celsius, Fahrenheit and Kelvin use offset formulas, and the working panel shows the exact formula that ran instead of a misleading multiplier.

  • Sensible rounding

    Results use up to six significant digits with grouped thousands, which is precise enough for practical work and readable at a glance.

  • No network, no account

    Conversion runs entirely in the browser, so the value never leaves the device and there is nothing to sign in to.

How to use Unit Converter

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose a unit family

    Select Length, Mass, Temperature, Volume or Speed at the top of the tool.

  2. 02

    Enter the value and source unit

    Type the number and pick the unit it is currently in; negative values are accepted, mainly for temperatures.

  3. 03

    Pick the target unit

    Choose the unit you want the result in and the converted value appears immediately.

  4. 04

    Check the all-units table

    The table shows the same value in every unit of the family, including the one you entered, which makes the result easy to verify.

  5. 05

    Swap or reset

    Press Swap units to reverse the conversion with the answer as the new input, or Reset to clear the value and start again.

How this tool works

Works with
Units
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • US customary volume units are used for fluid ounces, cups and gallons; UK imperial volumes differ and are not covered.
  • Results are rounded for display at up to six significant digits, so very small or very large values may differ slightly from the exact definition.
  • Only unit conversion is performed: no currency, timezone, data-size or cooking-density conversions are included.

Privacy and file handling

Every calculation runs in your browser with JavaScript. The values and units you select are never uploaded, stored or logged, and no request is made to a server while you convert.

Read the full privacy policy

Unit Converter FAQ

Short, direct answers to the questions people ask before using this tool.
What is the difference between mass and weight in this converter?
Mass units such as milligrams, grams, kilograms, ounces and pounds measure how much matter is in an object, while weight is a force that changes with gravity. The converter covers mass units, which is what scales and recipes mean in everyday language.
Why is temperature different from the other unit families?
Celsius, Fahrenheit and Kelvin do not share a single multiplier: each scale has a different zero point, so converting needs an offset formula such as °F = °C × 9/5 + 32. The tool shows the formula it used so the result can be checked by hand.
How many decimal places should I keep?
The tool shows up to six significant digits, which is more than most physical measurements justify. For a recipe or a form, round to the precision of the input; for engineering work, keep the digits your tolerance allows rather than the full display value.
Are US and imperial fluid ounces the same?
No. This converter uses US customary volume units: one US fluid ounce is 29.5735 mL and one US gallon is 3.785 L. An imperial UK fluid ounce is about 28.413 mL and a UK gallon is about 4.546 L, so check which system a source uses.
Why does one mile not equal exactly 1.6 km?
The international mile is defined as exactly 1,609.344 meters and a kilometer is 1,000 meters, so one mile is 1.609344 km. Rounding to 1.6 km is convenient for mental arithmetic but introduces an error of about half a percent.
Can I convert negative values?
Yes, the converter accepts negative numbers. That is mainly useful for temperatures, and it also lets you keep a signed measurement when working with offsets. A value below absolute zero is flagged with a warning because it is not physically meaningful.
What is a knot and how fast is it?
One knot is one nautical mile per hour, which is exactly 1.852 km/h, so 100 knots is about 185 km/h. It remains the standard speed unit for ships and aircraft because nautical miles line up with the Earth's coordinates.
Is the unit converter free and private?
It is free, needs no account, and every conversion runs locally in your browser. The value you type is never uploaded, stored or logged, and it disappears when you close the page.