Is one inch exactly 2.54 cm?

Yes. The inch is defined as exactly 2.54 centimeters, so that conversion has no rounding error.

Why do US and UK gallons differ?

They are historically different units. A US gallon is about 3.785 liters, while a UK imperial gallon is about 4.546 liters, so always note which system you are using.

Does the unit converter upload my numbers?

No. Conversions are calculated locally in your browser and nothing is uploaded.

Explainer1 min readUpdated June 29, 2026

Metric vs imperial units explained

Short answer

Metric (meters, grams, liters) is a decimal system used by most of the world; imperial (feet, pounds, gallons) is used mainly in the United States. Converting between them is just multiplying by a fixed factor, such as 1 inch = 2.54 cm.

Two systems

The metric system scales in powers of ten, so a kilometer is 1000 meters and a centimeter is one hundredth of a meter. The imperial system uses fixed but uneven steps, such as 12 inches to a foot and 3 feet to a yard, which makes mental math harder.

Conversions worth knowing

1 inch = 2.54 cm (exact)
1 foot = 0.3048 m (exact)
1 mile ≈ 1.609 km
1 pound ≈ 0.4536 kg
1 gallon (US) ≈ 3.785 liters
Celsius to Fahrenheit: multiply by 9/5 and add 32

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Watch the gallonA US gallon and a UK (imperial) gallon are different sizes. Confirm which one you mean before converting volumes.

Exact vs approximate

Some conversions are exact by definition, like 1 inch being 2.54 cm. Others are rounded, like a mile to kilometers. For engineering or science, keep the full precision; for everyday use, a rounded value is fine.