Length conversion calculators

How to choose and check a conversion

Length measures one dimension, such as height, width, depth, or distance. The meter is the SI base unit of length. Centimeters and millimeters are decimal fractions of a meter, while kilometers are used for longer distances. Inches, feet, yards, and miles belong to customary or imperial families.

For a quick reasonableness check, compare unit sizes before calculating. There are more centimeters than meters in the same length, so a meter-to-centimeter result should have a larger number. There are fewer miles than feet in the same distance, so a feet-to-miles result should have a smaller number.

Common mistakes include treating an area measurement as a length, mixing decimal feet with feet-and-inches notation, or rounding the input before conversion. A value such as 5.5 feet means five and one-half feet, not five feet five inches.

Accuracy and sources

Convertly keeps additional precision during calculation and rounds the display for readability. Match the final precision to the source measurement and the purpose of the answer. See our methodology and source policy for definitions, primary references, limitations, and correction procedures.

Exact definitions, estimates, and rounding

Some unit relationships are exact definitions, while a measured input is still limited by the instrument used to obtain it. A calculator can correctly apply an exact factor without making the original measurement more precise. Keep the original unrounded value, perform the conversion, and round the final result to a level appropriate for the task.

Use the stated formula to check the direction of the conversion. When possible, test a familiar value such as 1, 10, or 100 before relying on an unfamiliar result. For professional, regulated, health, safety, or contractual work, confirm the required convention and rounding rule in the controlling standard or document.