Free Online Unit Converter
Convert length, weight, temperature, volume, and more
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Why use Unit Converter
- Eight categories in one tool -- no need to open separate converters for temperature, data, and length.
- Exact mathematical factors (1 inch = 25.4 mm, not a rounded approximation) prevent compounding errors.
- Swap button reverses direction in one click without reselecting both dropdowns.
- Includes stones, knots, and nautical miles that simpler converters leave out.
How it works
Each category stores conversion factors relative to a base unit (meters for length, kilograms for weight, liters for volume). The tool multiplies the input by the source factor to reach the base, then divides by the target factor. Temperature is the exception -- Celsius, Fahrenheit, and Kelvin use dedicated formulas rather than simple multiplication. Results display to six significant digits via toPrecision(). The formula shown below the result is the direct multiplier derived by dividing the two factors.
About this tool
How many kilograms is 150 pounds? What is 72 degrees Fahrenheit in Celsius? Type the number, pick your units, and the answer appears while you are still typing. Eight categories -- length, weight, temperature, volume, area, speed, data storage, and time -- cover the conversions people actually look up. Metric and imperial are both supported, along with stones (UK body weight), knots (aviation and maritime), and the US vs imperial gallon distinction that trips up anyone following recipes across the Atlantic. Temperature uses the correct formulas rather than a lookup table. Data storage defaults to binary (1 KB = 1024 bytes), matching how operating systems report sizes. Time spans from milliseconds to years -- handy for timeout configs and SLA windows. Every result shows the exact conversion factor underneath so you can verify the math or drop it into a spreadsheet. A swap button reverses direction without reselecting both dropdowns.
How to use Unit Converter
- Pick a category. Click Length, Weight, Temperature, Volume, Area, Speed, Data, or Time.
- Choose source and target units. Select the unit you have in the left dropdown and the unit you want in the right dropdown.
- Type the value. Enter the number. The result updates as you type -- no submit button.
- Swap if needed. Click the Swap button to reverse direction (e.g., km to miles becomes miles to km) without reselecting units.
- Check the formula. Below the result, the exact factor or formula is shown (e.g., multiply by 0.621371). Copy it into your own spreadsheet if you need it.
Use cases
- Planning a US road trip from Australia and converting speed limits from km/h to mph.
- Scaling a UK recipe that lists butter in grams into US cups and ounces.
- Filling out a cloud infrastructure spec that requires memory in decimal gigabytes when the dashboard shows MiB.
- Calculating how many seconds are in a 7-day SLA window for a timeout config.
- Double-checking a spec sheet that mixes inches and millimeters before sending it to a machinist.
- Converting body weight from stones to kilograms for a fitness app that only accepts metric.
Frequently Asked Questions
Multiply by 9/5 and add 32. Example: 25°C * 1.8 + 32 = 77°F. Reverse: subtract 32 and multiply by 5/9.
Exactly 1.609344. Quick mental math: multiply km by 0.6 for a rough miles estimate, or multiply miles by 1.6 for rough km.
Metric units (meters, grams, liters) use base-10 prefixes -kilo means 1000, centi means 1/100. Imperial units (feet, pounds, gallons) use irregular conversion factors (12 inches in a foot, 16 ounces in a pound). Most countries use metric; the US, Myanmar, and Liberia still primarily use imperial for everyday measurements.
Both conventions exist. In computing (RAM, file systems), 1 KB = 1024 bytes (binary). In storage marketing (hard drives, SSDs), 1 KB = 1000 bytes (decimal). The IEC standard uses KiB (kibibyte) for 1024 and KB for 1000, but most people still say KB for both. This tool uses the 1024 (binary) convention, which matches how operating systems report file sizes.
All conversions use exact mathematical conversion factors (e.g., 1 inch = exactly 25.4 mm, 1 pound = exactly 0.45359237 kg). Results are displayed to 6 significant digits, which is more than sufficient for any practical purpose. Temperature conversions use the exact formulas, not approximations.
One US gallon equals exactly 3.785411784 liters. Conversely, one liter is about 0.264172 US gallons. Note that a UK (imperial) gallon is larger at 4.54609 liters. This tool uses US gallons, which is the standard in the United States.
Multiply the weight in pounds by 0.453592. For example, 150 lbs × 0.453592 = 68.04 kg. To convert the other way, multiply kilograms by 2.20462. Select Weight, choose pounds and kilograms, type your value, and the tool shows the result with 6 significant digits.
A US liquid gallon is 3.785 liters. A UK (imperial) gallon is 4.546 liters -about 20% larger. Fuel economy (miles per gallon) figures from UK and US sources are not directly comparable because they use different gallon sizes. This converter uses US gallons. If you need to convert UK mpg to US mpg, divide by 1.20095.
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, 98.6°F: (98.6 − 32) × 5/9 = 37°C. A quick mental shortcut: subtract 30 and halve it for a rough estimate (98.6 − 30 = 68.6, ÷ 2 ≈ 34°C, close enough for practical purposes). Use the Temperature tab above for exact results.
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