Unit Converter
Convert length, mass, volume, temperature, area and speed. Metric and US customary units, instant in your browser.
Result
Values may be rounded for display. Internal math uses standard double-precision floating-point numbers.
Everyday examples
Road trip distance
A sign shows 120 km. Convert to miles to compare with a US rental car odometer.
Recipe scaling
A European recipe lists 500 ml of milk. Switch to US cups when your measuring set is imperial.
Body weight
Clinic notes in kg, gym scale in lb: enter your weight and pick the units you need.
Room temperature
HVAC manual in °F, thermostat in °C: temperature uses offset formulas, not a simple multiplier.
Land area
Compare a 0.25 ha plot with listings quoted in acres for a rural purchase.
Speed limit
Translate 90 km/h into mph before driving in a country that posts limits in miles per hour.
How to use
Pick a category, enter a number, and choose the units to convert between. The result updates as you type. Use Swap to reverse the direction and keep the numeric value meaningful (for example after converting 10 km to miles, swap lets you edit in miles and see kilometres).
Quick steps
- Select a category (length, mass, volume, and others).
- Type the value you want to convert.
- Choose the source unit (From) and target unit (To).
- Read the large result and the equation line above it.
- Tap Swap if you want to invert units and continue from the converted number.
How it calculates
For length, mass, volume, area, and speed, each unit is stored as a factor to a base SI unit. The converter multiplies by the source factor and divides by the target factor.
Temperature is different: values are converted through Kelvin with fixed offsets for Celsius and Fahrenheit.
When should you use this?
Cooking and baking
Switch between grams and ounces, millilitres and cups, without guessing from memory.
Travel and maps
Compare kilometres and miles, litres per 100 km vs mpg, or local speed units.
School and work
Check homework, lab reports, or product specs when sources mix metric and US customary units.
Common mistakes
US vs UK gallons
Volume presets use US customary cups and gallons. UK imperial gallons are larger; do not mix them in recipes.
Treating °C like a ratio
Doubling Celsius does not double Fahrenheit. Always use a temperature category for heat values.
Rounding too early
Round for display, not in the middle of a chain of conversions, if you need audit-level accuracy.
| Scenario | Example input | Typical result | Real-world context |
|---|---|---|---|
| Marathon distance | 42.195 km → mi | ≈ 26.22 mi | Race programmes often list both units for international runners. |
| Checked baggage | 23 kg → lb | ≈ 50.7 lb | Airline limits are usually published in kg or lb depending on region. |
| Engine displacement | 2.0 l → US fl oz | ≈ 67.6 fl oz | Automotive specs may mix litres with US marketing units. |
| Freezing point | 0 °C → °F | 32 °F | Weather and HVAC references still mix scales in daily life. |
| Urban speed | 50 km/h → mph | ≈ 31.1 mph | Drivers crossing borders need a quick mental check of limits. |
Key terms
SI units
The International System of Units (SI) is the modern metric standard built around metre, kilogram, second, and kelvin.
Conversion factor
A fixed number that relates one unit to another when the quantities measure the same physical dimension.
US customary
Inch-foot-mile, pound, US fluid ounce, cup, and US gallon used in the United States for many everyday measures.
Offset scale
Temperature scales where zero is not the absolute zero point, so conversion needs addition and subtraction, not only multiplication.
Frequently Asked Questions
Accuracy, privacy, and what this tool can convert.