📏 Inches to CM Converter, Convert Inches to Centimeters

What is the inches to cm Converter?

The inch and the centimeter come from two different measuring systems. The inch is part of the imperial and US customary systems still used in the United States, the United Kingdom, and a few other places, while the centimeter is part of the metric system used almost everywhere else. For a long time the inch was defined in slightly different ways in different countries, which caused small but annoying discrepancies in engineering and trade.

That was fixed in 1959, when the international yard and pound agreement set the inch to exactly 2.54 centimeters. Because this is a definition and not a measurement, the factor is exact: there is no rounding hidden inside it. So the conversion is simply cm = inches x 2.54. A 6 inch phone screen is 6 x 2.54 = 15.24 cm, and a 36 inch curtain drop is 36 x 2.54 = 91.44 cm.

To go the other way, from centimeters to inches, you divide by the same factor: inches = cm / 2.54. So 30 cm is 30 / 2.54 = 11.811 inches. Because 1 cm is only about 0.3937 of an inch, centimeter values are always a larger number than the equivalent inch value, which is a quick sanity check that you multiplied and divided the right way round.

Many real measurements are not whole numbers of inches but fractions, such as 1/2 inch, 1/4 inch, or 3/8 inch, which is how rulers, tape measures, and woodworking plans are usually marked in the US. To convert a fraction of an inch, first turn it into a decimal (1/2 = 0.5, 3/8 = 0.375) and then multiply by 2.54 the same way, so 3/8 inch = 0.375 x 2.54 = 0.9525 cm. Heights are another common source of confusion, since they are usually written as feet and inches together, like 5 ft 9 in. Convert the feet to inches first (5 x 12 = 60), add the remaining inches (60 + 9 = 69), then multiply the total by 2.54.

Precision matters most when small errors add up. Cutting fabric, sizing a picture frame, or machining a part can go wrong if you round 2.54 down to 2.5 early in a calculation, because that 1.6 percent error scales with every inch. Keep the full factor of 2.54 until the very last step, then round the final answer to the precision your task actually needs. For everyday use, two decimal places (like 30.48 cm) is more than enough; for engineering or manufacturing, keep three or four.

When to use it

• Converting a TV, monitor, or phone screen size given in inches into centimeters for a wall space or bag.
• Working out clothing and body measurements when a size chart mixes inches and centimeters.
• Reading US furniture, curtain, or appliance dimensions and checking they fit a metric room plan.
• Doing school or engineering homework where a length must be expressed in the metric system.
• Converting a height given in feet and inches, such as 5 ft 9 in, into centimeters for a medical, visa, or sports form.
• Checking woodworking, sewing, or DIY plans that mix fractional inch measurements with a metric tape measure.

How to use the inches to cm Converter

1. Type the length in inches into the Inches field (it starts at 12 as an example).
2. Read the centimeter result, which updates instantly as you type.
3. To convert the other way, type a value into the Centimetres field to get inches.
4. For a fraction of an inch, convert it to a decimal first (1/2 = 0.5, 1/4 = 0.25) and type that decimal in.
5. Use the preset buttons for common sizes, or press Clear to start over.

Formula & method

Worked examples

Inches to centimeters conversion chart (exact, factor 2.54)

Centimeters to inches chart (reverse, divide by 2.54)

Common fractions of an inch in centimeters

Common mistakes to avoid

• Rounding the factor to 2.5 too early. The exact factor is 2.54, not 2.5. Using 2.5 introduces a 1.6 percent error that grows with the length: a 36 inch value comes out as 90 cm instead of the correct 91.44 cm. Keep 2.54 in the sum until the final step.
• Confusing the two directions. To get centimeters you multiply by 2.54; to get inches you divide by 2.54. Multiplying when you meant to divide turns 10 cm into 25.4 inches instead of the correct 3.937 inches. The cm value is always the bigger number.
• Mixing up centimeters and millimeters. There are 10 millimeters in a centimeter. 1 inch is 2.54 cm but 25.4 mm. Reading a metric ruler in the wrong unit gives an answer that is out by a factor of 10.
• Treating feet and inches as one number. A height like 5 feet 9 inches is not 5.9 inches. Convert it to inches first (5 x 12 + 9 = 69 in), then multiply by 2.54 to get 175.26 cm.
• Converting a fraction of an inch without a decimal step. A ruler mark like 3/8 inch cannot be multiplied by 2.54 directly as "3/8". Convert the fraction to a decimal first (3/8 = 0.375), then multiply: 0.375 x 2.54 = 0.9525 cm.
• Reporting more precision than the original measurement supports. A tape measure read to the nearest 1/8 inch cannot suddenly become accurate to four decimal places in centimeters. Round the converted result to match how precisely the original value was actually measured.

Glossary

Inch

A unit of length in the imperial and US customary systems, defined as exactly 2.54 centimeters since 1959.

Centimeter

A metric unit of length equal to one hundredth of a meter. Ten millimeters make one centimeter.

Conversion factor

The fixed number you multiply or divide by to move between units. For inches and centimeters it is exactly 2.54.

Imperial system

A system of units including inches, feet, and yards, still common in the US and UK.

Metric system

The decimal measuring system based on meters, centimeters, and millimeters used across most of the world.

Exact value

A number defined without rounding. Because 1 inch is defined as 2.54 cm, the factor carries no measurement error.

Fraction of an inch

A measurement such as 1/2, 1/4, or 3/8 inch, common on US rulers and tape measures. Convert to a decimal before multiplying by 2.54.

Significant figures

The digits in a number that carry meaningful precision. A converted result should not claim more precision than the original measurement had.

Frequently asked questions