Unit Converter
Convert between units of length, weight, volume, temperature, and area.
Results rounded to 4 decimal places. Click any result's ⇄ to make it the source.
- Millimeter (mm)—
- Centimeter (cm)—
- Meter (m)—
- Kilometer (km)—
- Foot (ft)—
- Yard (yd)—
- Mile (mi)—
- Nautical Mile (nmi)—
How to Use This Unit Converter
- Select a category from the tabs above.
- Choose units: Pick your “From” unit and “To” unit.
- Enter a value in either field. The other updates instantly.
- Swap units with the ⇄ button to reverse direction.
- Copy the result with the copy button.
Understanding Measurement Systems
The Metric System (SI)
- Developed in France during the 1790s.
- Based on powers of 10 (kilo = 1000, centi = 0.01, milli = 0.001).
- Used by most countries worldwide.
- Primary units: meter (length), gram (mass), liter (volume), Celsius (temperature).
The Imperial / US Customary System
- Evolved from English units used in the British Empire.
- US Customary differs slightly from British Imperial (especially volume).
- Primary units: inch/foot/mile (length), ounce/pound (mass), cup/gallon (volume), Fahrenheit (temperature).
- Still used in the United States, Liberia, and Myanmar.
Quick Reference
Length
| Conversion | Approximate Value |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 yard | 0.914 m |
| 1 mile | 1.609 km |
| 1 meter | 3.281 ft |
| 1 km | 0.621 mi |
Weight
| Conversion | Approximate Value |
|---|---|
| 1 ounce | 28.35 g |
| 1 pound | 453.6 g |
| 1 kg | 2.205 lb |
| 1 stone | 14 lb (6.35 kg) |
Volume
| Conversion | Approximate Value |
|---|---|
| 1 teaspoon | 5 mL |
| 1 tablespoon | 15 mL |
| 1 cup (US) | 237 mL |
| 1 pint (US) | 473 mL |
| 1 quart (US) | 946 mL |
| 1 gallon (US) | 3.785 L |
Temperature
| Description | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0 °C | 32 °F |
| Room temperature | 20–22 °C | 68–72 °F |
| Body temperature | 37 °C | 98.6 °F |
| Water boils | 100 °C | 212 °F |
Frequently Asked Questions
What is the difference between metric and imperial?
The metric system (SI) is based on powers of 10, using meters, grams, and liters. Imperial/US Customary uses inches, feet, pounds, and gallons with non-decimal relationships. Metric is used worldwide for science and by most countries; Imperial is mainly used in the US.
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 (or 1.8), then add 32. For example: 25 °C × 1.8 + 32 = 77 °F. To go the other way, subtract 32 then multiply by 5/9.
Why are there two different gallon sizes?
The US gallon (3.785 liters) and Imperial gallon (4.546 liters) diverged historically. The US adopted the older English wine gallon in 1707, while Britain standardized on a larger gallon in 1824. This affects all related measures (pints, quarts). This converter uses US customary volume units.
What is a nautical mile and why is it different?
A nautical mile (1,852 meters) equals one minute of latitude. It's used in aviation and maritime navigation because it relates directly to Earth's geometry, making navigation calculations simpler. A statute mile (1,609 meters) is the land mile.
What is a stone and where is it used?
A stone equals 14 pounds (6.35 kg). It's commonly used in the UK and Ireland for body weight. Saying “I weigh 11 stone” (154 lb / 70 kg) is standard in British English.
Notes & Disclaimers
- Precision: Conversions use standard factors. Displayed results are rounded to 4 decimal places; internal calculations maintain full precision.
- Temperature: Kelvin cannot be negative; values below absolute zero (0 K / −273.15 °C / −459.67 °F) are physically impossible and will show an error.
- Scientific use: For laboratory or engineering work requiring extreme precision, consult official NIST or BIPM standards and account for measurement uncertainty.