Units of Measurement Reference Guide

The International System of Units (SI, from French Système international d'unités) is the modern form of the metric system. It is the world's most widely used system of measurement for science, industry, and commerce. Its seven base units are the meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).

There are exactly 2.54 centimeters in one inch (1 in = 2.54 cm). This conversion is defined internationally and is used in all legal and scientific contexts.

Mass is a measure of the amount of matter in an object, typically measured in kilograms (kg) or pounds (lb). Weight is the force exerted on a mass due to gravity, measured in newtons (N) or pound-force (lbf). On Earth, weight and mass are often used interchangeably in everyday language, but they are scientifically distinct.

The three main scales are Celsius (°C), Fahrenheit (°F), and Kelvin (K).
°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9
K = °C + 273.15
Kelvin is used in scientific settings and does not have a "degree" symbol.

One acre equals 43,560 square feet or about 4,047 square meters. This unit is commonly used in the United States for land area measurements.

The US liquid gallon is about 3.785 liters, while the Imperial (UK) gallon is approximately 4.546 liters. This guide uses US customary units unless noted otherwise.

A nautical mile (nmi) is a unit used for air and sea navigation. It equals exactly 1,852 meters, or about 1.1508 statute miles. It is based on the Earth's circumference and is convenient for charting and navigation.

A kilobyte (KB) typically refers to 1,000 bytes (SI convention), while a kibibyte (KiB) equals 1,024 bytes (IEC binary prefix). Hard drive capacities are often advertised in SI prefixes, while operating systems frequently report in binary.