The Complete Unit Conversion Guide
Most of the world uses the metric system, while the United States mainly uses the US customary system (closely related to the older imperial system). This guide is a quick reference for converting between the two, with links to a dedicated calculator for every conversion below.
Metric vs. Imperial: The Short Version
The metric system (used almost everywhere outside the US) is based on units of 10 — meters, grams, and liters, scaled with prefixes like kilo- (×1,000) and centi- (×0.01). The US customary system uses units like miles, pounds, and gallons, most of which trace back to the older British imperial system and don't share a common base-10 scale. That mismatch is exactly why conversion tools are useful: there's no simple mental shortcut for most metric-to-imperial conversions.
Quick Reference Chart
| Category | Common Conversion | Calculator |
|---|---|---|
| Length | 1 mile = 1.60934 km | Miles to Kilometers |
| Length | 1 inch = 2.54 cm | Inches to Centimeters |
| Length | 1 foot = 0.3048 m | Feet to Meters |
| Weight | 1 lb = 0.453592 kg | Pounds to Kilograms |
| Weight | 1 oz = 28.3495 g | Ounces to Grams |
| Temperature | 0°C = 32°F | Celsius to Fahrenheit |
| Volume | 1 gallon = 3.78541 L | Gallons to Liters |
| Volume | 1 fl oz = 29.5735 mL | Fluid Ounces to Milliliters |
| Area | 1 acre = 0.404686 ha | Acres to Hectares |
| Area | 1 sq ft = 0.092903 m² | Square Feet to Square Meters |
| Speed | 1 mph = 1.60934 km/h | MPH to KM/H |