Metric to Imperial: The Only Conversion Table You Need

Why two measurement systems exist

The metric system was born in France in the 1790s, in the middle of the Revolution. The new government wanted measurement freed from royal body parts and local customs, so it defined the meter as one ten-millionth of the distance from the North Pole to the equator. Everything scales by tens — a kilometer is 1,000 meters, a centimeter is one hundredth of a meter — which is a big reason nearly every country adopted it.

Imperial units evolved over centuries in England and were standardized across the British Empire by the Weights and Measures Act of 1824: 12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile. The United States uses a close cousin called US customary units, inherited from older English units — which is why a US gallon (3.78541 L) is smaller than the British imperial gallon (4.54609 L).

Today only three countries — the United States, Liberia and Myanmar — have not officially made the metric system their standard, so converting between the two systems remains a daily necessity for travel, cooking, engineering and online shopping.

The conversion table

These factors are exact definitions, not approximations. Since an international agreement in 1959, the inch has been defined as exactly 2.54 centimeters, and the other length units are built from it (1 ft = 12 in, 1 yd = 36 in, 1 mi = 1,760 yd). The pound is defined as exactly 0.45359237 kilograms. The US gallon is defined as 231 cubic inches, which works out to 3.78541 liters.

To convert from imperial to metric, multiply by the factor. To go from metric to imperial, divide by it. Temperature is the exception — it needs the formulas further down, because the two scales do not share a zero point.

Converting step by step

The routine is always the same: get the quantity into a single unit, find the factor in the table, then multiply or divide. Worked through real examples:

Temperature needs a formula, not a factor

Lengths and weights convert with a simple multiplier because zero means the same thing in both systems — zero inches and zero centimeters are the same length. Temperature scales have different zero points: water freezes at 0 °C but 32 °F. So converting temperature means shifting by 32 and scaling by 9/5, because the span from freezing to boiling is 100 Celsius degrees but 180 Fahrenheit degrees.

Watch the order of operations. Going to Fahrenheit, scale first, then add 32. Going to Celsius, subtract 32 first, then scale.

Estimation tricks for daily life

Exact factors are for paperwork. For daily life, rounded versions are faster and stay within about 5% of the true value:

The Celsius shortcut — double and add 30 — drifts at temperature extremes: at 0 °C it predicts 30 °F instead of the true 32 °F. But across normal weather and cooking ranges it lands within about 4 degrees, which is plenty for deciding what to wear.

Frequently asked questions