Unit Converter Guide: How Conversions Work
Whether you're converting kilometers to miles, kilograms to pounds, or Celsius to Fahrenheit, every unit conversion follows the same underlying logic: multiply by a conversion factor equal to 1. This guide shows the method and the special cases where it breaks down.
The Factor-Label Method
The conversion factor is a fraction equal to 1, so multiplying by it changes the units without changing the quantity.
Example: to convert 5 miles to kilometers, multiply by 1.60934 (since 1 mile = 1.60934 km): 5 × 1.60934 = 8.05 km.
Common Conversion Factors
| Quantity | Conversion |
|---|---|
| Length | 1 mile = 1.60934 km; 1 inch = 2.54 cm |
| Weight | 1 lb = 0.453592 kg; 1 oz = 28.3495 g |
| Volume | 1 gallon (US) = 3.78541 L; 1 cup = 236.588 mL |
| Speed | 1 mph = 1.60934 km/h; 1 knot = 1.852 km/h |
Why Temperature Is Different
Most conversions use a single multiplier, but temperature between Celsius, Fahrenheit, and Kelvin requires a formula — because the zero points differ, not just the unit size.
You can't just "multiply by a factor" — you must also shift the zero point.
US gallons (3.785 L) and imperial gallons (4.546 L) are different. Always confirm which one a recipe or spec uses.
Put It Into Practice
Switch between length, weight, volume, temperature, speed, and more — pick a source and target unit and type your value.