Convert Metric Units of Length: A Simple Guide

This metric length converter changes a measurement from one unit of length to another, such as metres to centimetres or kilometres to miles. Enter a value and choose its starting and target units; the calculator returns the equivalent length, with the conversion factor and method explained below.

Formula

The conversion works by expressing the input in metres, then dividing by the number of metres in the target unit:

Target length = input value × source-unit factor ÷ target-unit factor

• Input value is the number entered, in the selected source unit.
• Source-unit factor is how many metres equal one source unit.
• Target-unit factor is how many metres equal one target unit.
• Target length is the converted value, expressed in the selected target unit.

For example, one kilometre has a factor of 1,000 because it equals 1,000 metres. One centimetre has a factor of 0.01 because it equals one hundredth of a metre. The second output, equivalent in metres, is an intermediate value that can also help check the result.

Worked Example

Using the calculator’s default values, convert 1 metre to kilometres. The source factor for metres is 1, and the target factor for kilometres is 1,000.

1. Convert the input to metres: 1 × 1 = 1 metre.
2. Convert metres to kilometres: 1 ÷ 1,000 = 0.001 kilometres.
3. The equivalent-in-metres output is 1 × 1 = 1 metre.

The calculator therefore returns 0.001 km and 1 m. The converted-length output is rounded to six decimal places; this example is exact at that precision.

Metric Length Units and Their Scale

The metric system is based on the metre. Prefixes show powers of ten, so moving between common metric units usually means multiplying or dividing by 10, 100, or 1,000. This consistent structure is why metric conversions can often be done by shifting a decimal point, provided the direction and number of places are correct.

• Kilometre (km): 1,000 metres; useful for longer distances such as roads or routes.
• Metre (m): the base unit for ordinary lengths, heights, and distances.
• Centimetre (cm): 0.01 metre, or 100 centimetres per metre; convenient for small objects and body measurements.
• Millimetre (mm): 0.001 metre, or 1,000 millimetres per metre; common for thicknesses and detailed dimensions.
• Micrometre (μm): one millionth of a metre, used for very small dimensions.
• Nanometre (nm): one billionth of a metre, used for extremely small scales.

The prefixes are not interchangeable. A millimetre is 1,000 times smaller than a metre, while a kilometre is 1,000 times larger. Writing the unit beside a number is a simple way to prevent confusion: 250 mm is not the same length as 250 cm.

Metric and US Customary Comparisons

Length conversion is also useful when a measurement is given in inches, feet, yards, or miles. These customary units do not follow the metric system’s powers-of-ten pattern, so use their exact metre equivalents rather than trying to shift a decimal point.

• 1 inch = 0.0254 metre, exactly.
• 1 foot = 0.3048 metre, exactly; 1 foot = 12 inches.
• 1 yard = 0.9144 metre, exactly; 1 yard = 3 feet.
• 1 mile = 1,609.344 metres, exactly; 1 mile = 5,280 feet.

For example, to convert 6 feet to metres, multiply 6 by 0.3048: the result is 1.8288 m. To convert 2 km to miles, divide 2,000 metres by 1,609.344 metres per mile, giving about 1.2427 miles. The calculator includes both metric and customary units so either direction can be handled with the same formula.

How to Use the Converter

1. Enter the length as a number. The default is 1 metre.
2. Select the unit that the entered number currently uses.
3. Select the unit you want the answer in.
4. Read the converted length and, if useful, the equivalent in metres.

The input must be a length, not an area or volume. For instance, metres convert to feet, but square metres measure area and cubic metres measure volume; those require different conversion relationships. The unit labels matter just as much as the number.

Common Conversion Mistakes and Precision

A frequent mistake is reversing the conversion factor. To convert a larger unit into a smaller unit, the numerical value usually increases: 2 m = 200 cm. To convert a smaller unit into a larger one, the value decreases: 200 cm = 2 m. The formula avoids relying on that intuition by consistently converting through metres.

• Check the source unit: confirm that the number is metres, centimetres, feet, or whichever unit you selected.
• Do not confuse abbreviations: km means kilometres, while cm means centimetres; the letters represent different prefixes.
• Keep enough precision during intermediate steps: round the final result, not each step, when accuracy matters.
• Match precision to the measurement: a calculator can display many decimal places, but that does not make an imprecise original measurement more precise.

Results are displayed to six decimal places. Very small or very large values may be easier to understand in a different unit—for example, 0.0005 m is 0.5 mm. Rounding is a display choice, not a change to the underlying conversion factor.

Frequently Asked Questions

How many centimetres are in a metre?
There are 100 centimetres in 1 metre. To convert metres to centimetres, multiply by 100; to convert centimetres to metres, divide by 100.

How many millimetres are in a centimetre?
There are 10 millimetres in 1 centimetre. Therefore, 1 cm equals 10 mm, and 1 m equals 1,000 mm.

How do I convert kilometres to miles?
Multiply kilometres by about 0.621371 to get miles. Equivalently, divide the number of kilometres by about 1.609344. The calculator uses the metre equivalents behind this relationship.

Is a metre longer than a yard?
Yes. One metre is about 1.0936 yards, while one yard is exactly 0.9144 metre. The difference is small enough that the units may seem similar, but they are not equal.

Why does my answer have so many decimal places?
Some unit pairs do not produce a short decimal result. The calculator shows up to six decimal places, but you can round the answer to suit the measurement’s required precision and keep the original units clear.

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in v | Length | m | 1 | 0
sel f | Convert from | km=1000, m=1, cm=0.01, mm=0.001, μm=0.000001, nm=0.000000001, mi=1609.344, yd=0.9144, ft=0.3048, in=0.0254
sel t | Convert to | km=1000, m=1, cm=0.01, mm=0.001, μm=0.000001, nm=0.000000001, mi=1609.344, yd=0.9144, ft=0.3048, in=0.0254
out r | Converted length | selected unit | v * f / t | 6
out b | Equivalent in metres | m | v * f | 6