Unit Conversion Guides
Convert length, weight, temperature, and more.
Understanding Unit Conversion
Unit conversion translates a measurement from one unit to another using a conversion factor. The key method: multiply by a fraction equal to 1 so unwanted units cancel out. This works for length, mass, volume, and most physical quantities — but temperature needs special formulas because its scales have different zero points.
The Conversion Factor Method
- Write the value with its unit as a fraction
- Multiply by a conversion factor (ratio of equivalent values)
- Cancel units until only the target unit remains
- Multiply and divide the numbers
Convert 5 kilometers to meters:
5 km × (1000 m / 1 km) = 5000 m
Length & Distance Conversions
| From | To | Multiply by | Exact? |
|---|---|---|---|
| Meters | Feet | 3.28084 | Yes (1 ft = 0.3048 m) |
| Kilometers | Miles | 0.621371 | Yes |
| Inches | Centimeters | 2.54 | Yes |
| Yards | Meters | 0.9144 | Yes |
| Miles | Kilometers | 1.60934 | Yes |
Example: 10 meters to feet = 10 × 3.28084 = 32.81 ft
Mass & Weight Conversions
Note: Mass (kg) and weight (force in newtons) are different. Everyday "weight" conversions assume standard gravity.
| From | To | Multiply by |
|---|---|---|
| Kilograms | Pounds | 2.20462 |
| Pounds | Kilograms | 0.453592 |
| Ounces | Grams | 28.3495 |
| Metric tons | US tons | 1.10231 |
Example: 70 kg to pounds = 70 × 2.20462 = 154.32 lb
Temperature Conversions
Temperature cannot be converted by a simple ratio — the scales have different zero points. Use these formulas:
°C = (°F − 32) × 5/9
K = °C + 273.15
| °C | °F | Description |
|---|---|---|
| 0 | 32 | Water freezes |
| 20 | 68 | Room temperature |
| 37 | 98.6 | Body temperature |
| 100 | 212 | Water boils (sea level) |
Example: 25°C to °F = (25 × 9/5) + 32 = 77°F
Volume, Area & Science Units
| Quantity | Common units | SI unit |
|---|---|---|
| Volume | L, mL, gallon, cup, m³ | m³ (1 L = 0.001 m³) |
| Area | m², ft², acre, hectare | m² |
| Pressure | Pa, bar, psi, atm | Pascal (Pa) |
| Energy | J, kJ, cal, kWh, BTU | Joule (J) |
| Speed | m/s, km/h, mph | m/s |
SI Prefixes (Quick Reference)
| Prefix | Symbol | Factor |
|---|---|---|
| kilo | k | × 10³ |
| centi | c | × 10⁻² |
| milli | m | × 10⁻³ |
| micro | μ | × 10⁻⁶ |
| nano | n | × 10⁻⁹ |
Common Conversion Mistakes
- Inverting the factor: meters→feet uses ×3.28, not ÷3.28
- Treating °C/°F as ratios: 20°C is NOT twice as hot as 10°C in absolute terms
- Confusing mass and weight: kg is mass; lb is often used as mass in everyday contexts
- US vs UK gallons: US gallon = 3.785 L; UK (imperial) gallon = 4.546 L
- Binary vs decimal GB: 1 GiB = 1024 MiB; 1 GB often means 10⁹ bytes in storage marketing
Frequently Asked Questions
Further Reading
Unit Conversion Made Easy (full article) · All Unit Converters