Conversions & Units · Glossary
What is Metric vs. Imperial?
Quick definition
Metric (SI) and Imperial (US customary) are the two main measurement systems. They differ in base units and conversion factors.
Full explanation
The metric system (SI) is the international standard, used by all countries except the US, Liberia, and Myanmar. It is decimal-based: 1 km = 1,000 m, 1 kg = 1,000 g. Imperial (or US Customary) uses older English units: inches, feet, pounds, gallons. Common conversions: 1 inch = 2.54 cm, 1 foot = 0.3048 m, 1 pound = 0.4536 kg, 1 gallon = 3.785 L. Within the US, fluid ounces, cups, pints, quarts, and gallons differ from their UK counterparts. The UK officially uses metric for most things but pints and miles persist culturally. Conversions are critical in science, engineering, cooking, and international trade.
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Last reviewed: June 15, 2026 • Category: Conversions & Units