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Length Converter

Length is measured in two different systems, and they meet constantly in everyday life. Recipes, sewing patterns, and schoolwork usually use the metric system — millimetres, centimetres, metres, and kilometres — while road signs, heights, and room sizes in the United States use the imperial system — inches, feet, yards, and miles. A phone screen is sold in inches, a piece of furniture is listed in centimetres, a running race is 5 kilometres or 3.1 miles depending on where you live, and a person's height might be written as 5 feet 9 inches or 175 cm. This free length converter moves between all eight units instantly. Type in a value, pick the unit you have and the unit you want, and the result appears at once, along with the same length expressed in every other unit in the table below. There is nothing to install and nothing to sign up for, and every conversion runs entirely in your browser.

How to Use This Converter

1. Enter your value in the first box. The converter starts with 100, but you can type any number, including decimals such as 5.5 or 175.5.
2. Choose the unit you have from the From dropdown — millimetres, centimetres, metres, kilometres, inches, feet, yards, or miles. This is the unit your measurement is currently in.
3. Choose the unit you want from the To dropdown. The result updates instantly, every time you type or change either dropdown, with no button to press.
4. Read the big result, then check the full table to see the same length in all eight units at once. If you need the reverse conversion, tap Swap Units and the two units trade places.

Worked Example

100 cm = 39.37 inches. The inch is defined as exactly 2.54 cm, so divide 100 by 2.54 and you get 39.3701, which rounds to 39.37 inches. The same length is also 1,000 mm, 1 m, 3.28 feet, and 1.09 yards — all shown in the results table when you enter 100 cm.

1 mile = 1.609 km. A mile is exactly 1,609.344 metres. Divide by 1,000 to change metres into kilometres and you get 1.609344 km, usually written as 1.609 km. That is why a 5 km race is about 3.11 miles: 5 divided by 1.609 is 3.107, rounded to 3.11.

1 foot = 30.48 cm. A foot is exactly 12 inches, and each inch is 2.54 cm, so 12 × 2.54 = 30.48 cm. This is the number to remember when converting heights: a person who is 6 feet tall is 6 × 30.48 = 182.88 cm, about 183 cm. Likewise, 12 inches make exactly 1 foot, and 3 feet make exactly 1 yard, which is 91.44 cm. Once you know the three anchor facts — 1 inch is 2.54 cm, 1 foot is 30.48 cm, and 1 mile is 1.609 km — you can check any length conversion by hand and spot a wrong answer immediately.

Tips for Accurate Length Conversions

The most common length mistake is mixing up centimetres and millimetres. There are 10 millimetres in a centimetre, so a measurement written as 150 mm is only 15 cm — move the decimal point one place, not two. The next most common mistake is treating feet and inches as decimals: 5 feet 9 inches is not 5.9 feet, it is 5 feet plus 9 inches, which is 69 inches or 175.26 cm. If a height is given in feet and inches, convert the whole thing to inches first (feet × 12, then add the inches) and convert from there.

Remember that metric steps are all powers of ten — 10 mm in a cm, 100 cm in a metre, 1,000 m in a kilometre — while imperial steps are irregular: 12 inches in a foot, 3 feet in a yard, and 1,760 yards in a mile. That irregularity is exactly why a converter helps. For rough estimates, remember that 1 inch is about 2.5 cm, 1 metre is about 3.3 feet, and 1 kilometre is about 0.62 miles; for anything you will cut, sew, build, or buy, use the exact result from the converter instead of the rough figure. Finally, watch your rounding: keep at least two decimal places for everyday use, and keep more when the result feeds into another calculation, because rounding early is how small errors grow into wrong cuts and wrong orders.

Frequently Asked Questions