How to Convert Inches, Feet and Celsius: A Guide to Everyday Unit Conversions

Published November 7, 2026 · 6 min read

A shelf listed in inches, a height given in feet, an oven set in Fahrenheit: these conversions come up all the time, and they are the kind of thing most people look up rather than remember. We added a free unit converter for exactly these cases. This guide covers the formulas behind it, the shortcuts worth memorizing, and the mistakes that catch people out.

Inches and centimeters

One inch is exactly 2.54 centimeters. That is the definition of the inch, not a rounded figure, so the conversion is a single multiplication or division:

Feet and centimeters

A foot is 12 inches, so one foot is 12 × 2.54 = 30.48 centimeters, also exact:

Heights in feet and inches

Heights are usually written in two parts, like 5'11", which needs one extra step. The easiest route is to turn everything into inches first, because a foot is always 12 inches:

The inches converter handles both of these. Work out the total inches, then type that number in.

Common lengths at a glance

Celsius and Fahrenheit

Temperature takes two steps, because the scales differ in both size and starting point. A Celsius degree is 9/5 the size of a Fahrenheit degree, and water freezes at 0 °C but 32 °F:

The order matters. Going to Fahrenheit, you multiply first and add 32 last. Going to Celsius, you subtract 32 first and multiply last.

Oven temperatures

Recipes rarely use the exact conversion. They round to a number that is easy to set on the dial, as this table shows:

Why length is a ratio and temperature is not

Inches and centimeters always have the same ratio, 1 : 2.54. Double the inches and you double the centimeters, and zero inches is zero centimeters. That makes any length conversion a proportion you can solve like any other:

Temperature does not work this way, because 0 °C is not 0 °F. Compare 10 °C, which is 50 °F, with 20 °C, which is 68 °F. The Celsius figure doubled, but the Fahrenheit figure did not. So 10 : 50 and 20 : 68 are not equal ratios, and the ratio calculator cannot convert temperatures. You need the temperature converter or the formula above. For more on setting up proportions, see our guide to cross-multiplication.

Shortcuts you can do in your head

These are estimates, so use the exact figures for anything you are cutting, building or ordering.

The temperature shortcut suits weather, but it drifts at higher temperatures. It turns 180 °C into 390 °F when the real answer is 356 °F, so do not use it for ovens.

Common mistakes to avoid

1. Reading decimal feet as feet and inches

5.5 feet is not 5'5". The decimal part is a fraction of a foot, so 0.5 feet is 6 inches and 5.5 feet is 5'6". Likewise, 5'11" is about 5.92 feet, not 5.11 feet. If you enter a height into the feet converter, use the decimal form or convert via total inches as shown above.

2. Multiplying when you should divide

A quick sense check catches this one. A centimeter is smaller than an inch, so the number of centimeters should always be larger than the number of inches. If your 10-inch shelf came out at 3.94 cm, you divided instead of multiplied.

3. Adding 32 to a temperature change

The 32 only applies to actual temperatures, not differences between them. A rise of 10 °C is a rise of 10 × 9/5 = 18 °F, not 50 °F. If the forecast says it will be 10 °C warmer tomorrow, that means 18 °F warmer.

4. Rounding too early

Using 2.5 instead of 2.54 feels harmless, but the error grows with the measurement. For 100 inches, it gives 250 cm instead of 254 cm, which is 4 cm off. That is enough to stop a piece of furniture fitting in an alcove.

Frequently asked questions