Length Unit Converter

What problem does a length converter solve?

Two measurement families share the world's roads, shops and workshops. Most countries use the metric system, built on metres, while the United States relies heavily on imperial-style units such as miles, feet and inches, and the United Kingdom uses a mixture of both. Any time you read a recipe for a bookshelf, check a hotel's distance from the airport, buy fabric from an overseas seller or follow a running plan, you may need to move between them. This converter handles eight units: metres, kilometres, centimetres, millimetres, miles, yards, feet and inches. Pick the unit you have, pick the unit you want, enter the value, and the result appears, shown to six decimal places.

How the conversion works

Every length unit here is defined as an exact multiple or fraction of the metre. The converter takes your value, converts it to metres, then converts from metres into the target unit. Using a common base avoids having a separate formula for every pair of units, which would be 56 combinations for eight units.

The key point is that the imperial units are now defined in terms of the metre. Since an international agreement on the yard and the pound in 1959, one yard is exactly 0.9144 metres. That makes the other values exact as well, because a foot is a third of a yard and an inch is a twelfth of a foot.

Unit	Equivalent in metres
1 millimetre	0.001 m
1 centimetre	0.01 m
1 metre	1 m
1 kilometre	1000 m
1 inch	0.0254 m
1 foot	0.3048 m
1 yard	0.9144 m
1 mile	1609.344 m

To convert from unit A to unit B, multiply by the metre value of A and divide by the metre value of B. For example, feet to centimetres is value x 0.3048 / 0.01, which equals value x 30.48.

How to use the converter step by step

1. Enter the number you want to convert in the value field.
2. Select the unit that number is currently in.
3. Select the unit you want to convert to.
4. Press Convert and read the result. It is rounded to six decimal places, so very small or very large values still show useful detail.
5. If you need to compare several measurements, repeat with each one, keeping the target unit the same.

Worked examples

Example 1: a five mile walk

You plan a 5 mile hike and your map app shows kilometres. Five miles is 5 x 1609.344 = 8046.72 metres, which is 8.04672 kilometres. So you can plan for roughly 8 kilometres.

Example 2: a person's height

Someone is 5 feet 10 inches tall. Convert everything to inches first: 5 x 12 + 10 = 70 inches. Then 70 x 0.0254 = 1.778 metres, or 177.8 centimetres. You can also check it with the other route: 5 feet is 1.524 m and 10 inches is 0.254 m, and 1.524 + 0.254 = 1.778 m.

Example 3: a sports field

An American football pitch is often described in yards. A distance of 100 yards equals 100 x 0.9144 = 91.44 metres. This is close to, but not the same as, a 100 metre sprint, which is a common source of casual confusion.

Example 4: a marathon

A marathon is 26.2 miles in round figures. Multiply 26.2 by 1.609344 and you get about 42.1648 kilometres. The official distance is usually quoted as 42.195 kilometres, because the 26.2 mile figure is itself rounded from 26 miles 385 yards.

Example 5: small parts

A screw is 12.7 millimetres long. Divide by 25.4 and the length is exactly half an inch. This conversion between millimetres and inches turns up often in hardware and electronics.

A brief history of metric and imperial units

The metric system came out of the French Revolution, when scientists proposed a decimal system of measures that could be shared by everyone and derived from nature. The metre was originally linked to the size of the Earth, and it has since been redefined with increasing precision. Today it is defined using the speed of light. The decimal structure is its great strength, because moving between millimetres, centimetres, metres and kilometres only needs powers of ten.

Imperial units developed over centuries from older, regional measures, many based on body parts and everyday objects: a foot, a yard, a mile derived from Roman paces. They were standardised in the British Empire and later adopted in the United States as "customary" units. Small differences between national versions persisted until the 20th century, when the agreement mentioned earlier fixed the yard to the metre. That is why today every imperial length is, strictly, defined from a metric value. The two systems still feel different to use, since imperial conversions involve factors like 12, 3 and 1760 instead of 10.

Because every factor is exact, the only rounding comes from the six decimal places shown. Converting a value and then converting it back will usually return the number you started with, give or take the last displayed digit.

Tips and best practices

• Use the right precision. For a hike, two decimals are plenty. For machining or engineering drawings, keep the full six.
• Convert once, at the end. If you add several lengths, add them in the same unit first and convert the total, rather than converting and rounding each one.
• Keep memorable anchors. One inch is 2.54 cm, one kilometre is about 0.62 miles, and one metre is slightly longer than one yard.
• Sanity check the direction. Converting to a smaller unit should make the number bigger, and converting to a larger unit should make it smaller.
• Double check mixed units. Heights like 5 feet 10 inches need to be turned into one unit before using the tool.

Common mistakes to avoid

• Mixing up miles and kilometres, which differ by roughly 60 percent.
• Treating a yard as equal to a metre. A metre is about 9 percent longer.
• Entering 5.10 for 5 feet 10 inches. A decimal foot is not the same as feet and inches, since 0.10 feet is only 1.2 inches.
• Rounding too early in a multi-step calculation.
• Reading a result without checking which unit is selected on each side.
• Forgetting that nautical miles and survey feet are different units and not covered here.

Who benefits from this tool

Travellers who face road signs in unfamiliar units, runners and cyclists comparing training plans, and students solving physics or geography problems all rely on conversions like these. Online shoppers can compare product dimensions from different countries. Builders, carpenters and hobbyists often work with plans that mix units. Designers and developers sometimes need physical sizes alongside screen measurements; for related technical conversions, see the Hex to RGB Converter. For other everyday unit changes, use the Temperature Converter, and for working with ratios the Percentage Calculator is a good companion. You can also browse our other free tools.

Privacy and safety

All conversions happen directly in your browser. The numbers you type are not sent to a server or stored, so you can use the tool for private projects, quotes and plans without any concern.

Limitations

The converter supports eight units only. It does not handle area or volume, nautical miles, light years, or unusual historical units. Results are rounded to six decimal places, which is more than enough for everyday needs, but it is not a replacement for certified measurement in surveying or engineering. It also converts one value at a time and does not parse inputs like "5 ft 10 in". Convert the parts to a single unit yourself first.

Frequently asked questions

How many metres are in a mile?

One mile is exactly 1609.344 metres, which is 1.609344 kilometres.

How many centimetres are in an inch?

One inch is exactly 2.54 centimetres, because it equals 0.0254 metres.

Is a yard the same as a metre?

No. A yard is 0.9144 metres, so a metre is a little longer, at about 1.0936 yards.

How do I convert feet and inches to metres?

Convert the whole measurement to inches by multiplying the feet by 12 and adding the inches, then multiply by 0.0254. For example, 6 feet 2 inches is 74 inches, or 1.8796 metres.

Why are the results shown with six decimals?

Six decimals keep small values accurate, such as converting millimetres to miles. You can round the answer further for everyday use.

Are these conversion factors exact?

Yes. The imperial units listed here are defined exactly in terms of the metre, so the factors are exact, not approximations.

Can the tool convert area or volume?

No. It only converts lengths and distances.

Does it work offline or store my input?

The calculation runs in your browser and nothing you enter is stored or sent anywhere.

In short

Metric and imperial units can feel like two languages, but they are linked by exact, fixed values. Keep the table handy, let the converter do the arithmetic, and choose a sensible level of precision for your task.