Unit Conversion Calculator
Convert between any units of length, weight, temperature, area, volume, and speed. Instant results.
What Is a Unit Conversion Calculator?
A unit conversion calculator transforms measurements between different systems — metric (used by most countries) and imperial/US customary (used in the United States, UK, and a few others). Whether you're converting kilometers to miles, kilograms to pounds, Celsius to Fahrenheit, or liters to gallons, this calculator handles all common conversions instantly without manual math.
Unit conversions appear in everyday life: cooking recipes from international sources, travel planning across countries, fitness tracking, scientific calculations, construction measurements, and academic homework. This free unit converter works for length, weight, temperature, volume, area, speed, and more — no signup or downloads required.
For other measurement-related calculations, use our Concrete Calculator for construction units or Percentage Calculator for percentage-based conversions.
Common Unit Conversions Reference
Quick conversion factors for the most frequently needed unit changes:
Length Quick Reference
| From | To | Multiply By | Example |
|---|---|---|---|
| Inches | Centimeters | 2.54 | 10 in = 25.4 cm |
| Feet | Meters | 0.3048 | 6 ft = 1.83 m |
| Yards | Meters | 0.9144 | 100 yd = 91.44 m |
| Miles | Kilometers | 1.609 | 50 mi = 80.45 km |
| Centimeters | Inches | 0.3937 | 170 cm = 66.9 in |
| Meters | Feet | 3.281 | 2 m = 6.56 ft |
| Kilometers | Miles | 0.6214 | 100 km = 62.14 mi |
Weight Quick Reference
| From | To | Multiply By | Example |
|---|---|---|---|
| Pounds (lb) | Kilograms (kg) | 0.4536 | 150 lb = 68.04 kg |
| Kilograms (kg) | Pounds (lb) | 2.205 | 70 kg = 154.3 lb |
| Ounces (oz) | Grams (g) | 28.35 | 8 oz = 226.8 g |
| Grams (g) | Ounces (oz) | 0.0353 | 500 g = 17.64 oz |
| Tons (US) | Kilograms (kg) | 907.185 | 1 ton = 907.2 kg |
| Stones (UK) | Kilograms (kg) | 6.350 | 12 stone = 76.2 kg |
Temperature Reference
Temperature conversion uses formulas rather than simple multiplication:
- Celsius to Fahrenheit: °F = (°C × 9/5) + 32
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9
- Celsius to Kelvin: K = °C + 273.15
- Kelvin to Celsius: °C = K − 273.15
| Description | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Water freezes | 0° | 32° | 273.15 |
| Room temperature | 20° | 68° | 293.15 |
| Body temperature | 37° | 98.6° | 310.15 |
| Hot day | 35° | 95° | 308.15 |
| Water boils | 100° | 212° | 373.15 |
Volume and Liquid Conversions
| From | To | Multiply By | Example |
|---|---|---|---|
| Gallons (US) | Liters | 3.785 | 10 gal = 37.85 L |
| Liters | Gallons (US) | 0.2642 | 50 L = 13.21 gal |
| Gallons (UK) | Liters | 4.546 | 10 UK gal = 45.46 L |
| Quarts | Liters | 0.946 | 4 qt = 3.78 L |
| Fluid ounces (US) | Milliliters | 29.574 | 8 fl oz = 236.6 mL |
| Cups | Milliliters | 236.588 | 2 cups = 473 mL |
Area Conversions
| From | To | Multiply By |
|---|---|---|
| Square Feet | Square Meters | 0.0929 |
| Square Meters | Square Feet | 10.764 |
| Acres | Hectares | 0.405 |
| Acres | Square Meters | 4046.86 |
| Square Miles | Square Kilometers | 2.59 |
| Bigha (India) | Square Meters | 2529.3 (varies) |
Speed Conversions
| From | To | Multiply By |
|---|---|---|
| Miles per hour (mph) | Kilometers per hour (km/h) | 1.609 |
| Kilometers per hour | Miles per hour | 0.6214 |
| Meters per second | Kilometers per hour | 3.6 |
| Knots | Kilometers per hour | 1.852 |
How to Use This Unit Converter
- Select category — Length, weight, temperature, volume, etc.
- Choose "From" unit — The unit you have
- Choose "To" unit — The unit you need
- Enter the value — Number you want to convert
- View result instantly — Converted value with precision
Why Different Countries Use Different Units
The world divides primarily into two measurement systems:
Metric System (SI): Used by ~95% of countries worldwide including all of Europe, China, India, Brazil, Russia. Based on powers of 10, making calculations intuitive. Standardized by the International System of Units.
Imperial/US Customary: Used primarily by the United States, plus partial usage in UK and Liberia. Originated from British weights and measures. Uses ounces, pounds, inches, feet, gallons, miles.
The differences exist for historical reasons. While the US officially adopted metric in 1975, day-to-day life still uses imperial. UK uses metric in science and law but imperial in road signs and daily life.
Common Unit Conversion Mistakes
- Confusing US and UK gallons: US gallon = 3.785 L, UK gallon = 4.546 L (20% difference!)
- Mixing fluid ounces with weight ounces: Fluid oz measures volume, oz measures weight
- Forgetting temperature is not multiplicative: 0°C is not 0°F (it's 32°F)
- Rounding too early: Round only at the final step for accuracy
- Confusing kg and pounds in cooking: Most international recipes use grams/kg
- Mph vs km/h on road signs: Critical for international driving
- Area conversions: Square units convert with factor squared (not just multiplied)
Practical Applications
- International travel: Converting currencies, distances, fuel prices, weather temperatures
- Cooking international recipes: Converting cups to grams, Fahrenheit ovens to Celsius
- Fitness tracking: Pounds to kilograms, miles to kilometers, inches to centimeters
- Construction projects: Square feet to square meters, gallons to liters of paint
- Academic homework: Physics, chemistry, biology calculations across unit systems
- Online shopping: US sizes (clothing, shoes) vs European/Indian sizes
- Scientific research: Converting research units across publications
- Engineering: Working with international clients across different standards
FAQs
What is the difference between metric and imperial?
Metric (SI) uses meters, kilograms, litres. Imperial uses feet, pounds, gallons. Most countries use metric; the US primarily uses imperial.
How do I convert temperature?
Celsius to Fahrenheit: multiply by 9/5 and add 32. Celsius to Kelvin: add 273.15.