Free Online Unit Converters for Everyday Measurements
Convert measurements between commonly used units for length, weight, temperature, area, volume, speed and more. Unit converters help make different measurement systems easier to compare without calculating every conversion by hand.
Choose the quantity you want to convert, enter the value and select the starting and target units. Check the units, conversion formula and rounding precision whenever accuracy matters.
Unit Converters for Common Measurements
Choose a converter based on the quantity and units you have. Each individual tool should explain the supported units, conversion factors and any special rules.
Length Converter
Convert metres, kilometres, centimetres, millimetres, inches, feet, yards and miles using the appropriate conversion factors.
Open converter →Weight Converter
Convert common mass units such as kilograms, grams, milligrams, pounds and ounces. Choose mass rather than force units when appropriate.
Open converter →Temperature Converter
Convert Celsius, Fahrenheit and Kelvin using the correct formulas, including offsets rather than a simple multiplier alone.
Open converter →Area Converter
Convert square metres, square feet, square kilometres, acres, hectares and other supported area units.
Open converter →Volume Converter
Convert litres, millilitres, cubic metres, US gallons and other volume units. Check which gallon definition is being used.
Open converter →Speed Converter
Convert kilometres per hour, miles per hour, metres per second and knots for suitable travel and measurement applications.
Open converter →Time Unit Converter
Convert seconds, minutes, hours and days using defined time-unit relationships. Calendar months and years need separate rules.
Open converter →Pressure Converter
Convert pascals, kilopascals, bar, standard atmospheres and other supported pressure units.
Open converter →Energy Converter
Convert joules, kilojoules, calories, kilocalories and kilowatt-hours while checking the intended energy unit.
Open converter →Power Converter
Convert watts, kilowatts and supported horsepower definitions for appropriate mechanical and electrical applications.
Open converter →Data Storage Converter
Convert bytes, kilobytes, megabytes and larger units. Check whether decimal SI or binary IEC units are intended.
Open converter →Angle Converter
Convert degrees and radians using the relationship between a full rotation, 360 degrees and 2π radians.
Open converter →Frequency Converter
Convert hertz, kilohertz, megahertz and gigahertz by applying the appropriate powers-of-ten factors.
Open converter →Fuel Economy Converter
Convert between supported fuel-economy units, taking care that miles per gallon and litres per 100 kilometres are not directly proportional.
Open converter →Density Converter
Convert compatible density units such as kilograms per cubic metre and grams per cubic centimetre.
Open converter →Pressure Units Converter
Compare commonly used pressure measurements, including bar, psi and pascals, using explicit conversion constants.
Open converter →Cooking Measurement Converter
Convert supported kitchen volume measures. Ingredient weight conversions require an ingredient-specific density or measurement standard.
Open converter →Number Base Converter
Convert numbers between binary, decimal, hexadecimal and other supported bases for maths and computing tasks.
Open converter →How Common Unit Conversions Work
Conversion formulas make the result easier to verify. The following examples use standard relationships; individual tool pages should state their precision and unit definitions.
| Conversion | Formula | Worked example |
|---|---|---|
| Metres to centimetres | cm = m × 100 | 2.5 m = 250 cm |
| Kilometres to metres | m = km × 1,000 | 3 km = 3,000 m |
| Kilograms to grams | g = kg × 1,000 | 1.2 kg = 1,200 g |
| Celsius to Fahrenheit | °F = (°C × 9/5) + 32 | 20°C = 68°F |
| Inches to centimetres | cm = inches × 2.54 | 10 inches = 25.4 cm |
| Kilometres per hour to metres per second | m/s = km/h ÷ 3.6 | 36 km/h = 10 m/s |
| Square metres to square feet | ft² ≈ m² × 10.7639 | 10 m² ≈ 107.639 ft² |
| Litres to millilitres | mL = L × 1,000 | 1.5 L = 1,500 mL |
Important Conversion Constants and Unit Rules
Some conversions use exact relationships, while others require a defined convention. Understanding the difference helps prevent misleading results.
Common exact relationships
- 1 inch = exactly 2.54 centimetres.
- 1 foot = 12 inches.
- 1 international mile = 1,609.344 metres.
- 1 kilogram = 1,000 grams.
- 1 litre = 1,000 millilitres.
- 1 hour = 60 minutes = 3,600 seconds.
Units that need extra care
- Temperature conversions require an offset as well as a scale factor.
- US and Imperial gallons have different volumes.
- Decimal and binary data-storage units are not interchangeable.
- Mass and weight describe different physical quantities.
- Calendar months do not have a fixed number of days.
- Fuel-economy conversions may be reciprocal rather than linear.
How to Convert Units Correctly
Use the same basic process for measurements in everyday life, study and work.
Select the quantity
Choose the correct measurement type, such as length, mass, temperature, volume or speed.
Choose both units
Set the original and target units. Check that they measure the same physical quantity.
Review the result
Check the formula, conversion factor and rounding precision before using the converted value.
Unit Converter FAQs
Answers to common questions about conversion formulas, accuracy and measurement standards.
What is a unit converter?
A unit converter changes a measurement from one unit to another compatible unit, such as metres to feet or kilograms to pounds, using a defined conversion relationship.
How accurate are online unit converters?
Accuracy depends on the formula, conversion constants, input precision and rounding method. Check the units and formula, particularly when using results for technical, professional or safety-related purposes.
What is the difference between mass and weight?
Mass measures the amount of matter and is commonly expressed in kilograms. Weight is a force and is measured in newtons. Everyday tools often label mass conversions as weight conversions, so check the actual units.
Why is converting Celsius to Fahrenheit different from converting metres to centimetres?
Length conversion uses a scale factor, while Celsius and Fahrenheit use both a scale factor and an offset. The formula is °F = (°C × 9/5) + 32.
What is the difference between a US gallon and an Imperial gallon?
A US liquid gallon is approximately 3.78541 litres, while an Imperial gallon is approximately 4.54609 litres. A converter should specify which gallon definition it uses.
Why can a converted result have many decimal places?
Some conversion factors produce repeating or long decimal values. A converter may display rounded results, but calculations should retain suitable precision before rounding the final answer.
Are megabytes and mebibytes the same?
No. A megabyte (MB) is commonly defined as 1,000,000 bytes, while a mebibyte (MiB) is 1,048,576 bytes. Always check whether a tool uses decimal SI or binary IEC units.
Can I convert volume into weight?
Only when you know the substance’s density and use compatible units. Equal volumes of different materials can have different masses, so a general volume conversion cannot determine weight by itself.
Are calendar months a fixed unit of time?
No. Calendar months have different lengths, so a month cannot be treated as a fixed number of days in every calculation. Use calendar-aware date tools when working with actual dates.
Need more practical online tools?
Explore the Tool Driver collection for calculators, date utilities, text tools and developer resources.