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Length Converter
To convert a length, multiply by the size of the starting unit in metres and divide by the size of the target unit. 100 yards is 100 × 0.9144 = 91.44 metres, exactly. This converter does that for ten units, including feet and inches, and shows the result in every unit at once.
Pick two units and type a length.
| Unit | Value |
|---|---|
| Millimetres | 91,440 mm |
| Centimetres | 9,144 cm |
| Metres | 91.44 m |
| Kilometres | 0.0914 km |
| Inches | 3,600 in |
| Feet | 300 ft |
| Feet and inches | 300 ft 0 in |
| Yards | 100 yd |
| Miles | 0.0568 mi |
| Nautical miles | 0.0494 nmi |
The figures above are an example: put in your own. With “feet and inches” as the From unit, type 5′ 7″, 5 ft 7 in or 5 7. Fractions such as 3/8 work in every unit. Worked out in this browser and kept there; nothing is sent anywhere.
Type a length, pick the unit it is in and the unit you want. The board shows the answer with its working, and the table shows the same length in all ten units, so you rarely need a second conversion.
A length converter changes a measurement from one unit of length to another, such as metres to feet, using the fixed factor between them. Since 1959 every inch-based unit has been an exact number of millimetres.
- No sign-up
- Nothing uploaded
- Exact factors
- Works offline
- Says when it rounds
Key facts
| Detail | Answer |
|---|---|
| Units | mm, cm, m, km, in, ft, feet and inches, yd, mi, nautical mi |
| Example | 100 yd = 91.44 m = 300 ft = 9,144 cm |
| Key factors | 1 in = 25.4 mm, 1 ft = 0.3048 m, 1 mi = 1,609.344 m, all exact |
| Arithmetic | Exact fractions; rounded once, for display |
| Refuses | Negative lengths, text that is not a length, more than a billion units |
| Where your numbers are kept | This browser only |
How to convert between length units
The converter does these steps; they also work by hand.
Type the length
A number, a decimal, a fraction such as 3/8, or feet and inches such as 5' 7".
Choose the unit it is in
The From list, including feet and inches.
Choose the unit you want
The To list; the board shows the result in that unit.
Set the decimal places
From 0 to 6. The working line keeps the exact digits.
Read the other units
The table gives the same length in all ten units.
Swap or copy
Swap units reverses the direction; Copy puts the result and the table on the clipboard.
Who uses a length converter
Anyone moving a measurement between a metric world and an imperial one.
DIY and building
A plan in feet and inches, a timber merchant in millimetres.
Online shopping
Furniture listed in inches for a room measured in centimetres.
Sport
A 100-yard field, a 400-metre track and a mile run on it.
Travel and maps
Kilometres on a sign, miles on the car, nautical miles on a chart.
Students
Unit questions checked, with the exact factor named.
Sewing and crafts
Patterns in inches, fabric sold by the metre.
Where each factor comes from, and why they are exact
Every unit on this converter is defined as an exact number of metres. None of the factors is a measurement that might be revised: they are definitions, so the converter can work in exact fractions and only round when it shows you the answer. The table gives each unit in metres and where that number comes from.
| Unit | In metres | Defined by |
|---|---|---|
| Millimetre (mm) | 0.001 m | SI prefix: a thousandth of a metre |
| Centimetre (cm) | 0.01 m | SI prefix: a hundredth of a metre |
| Metre (m) | 1 m | SI base unit, fixed by the speed of light |
| Kilometre (km) | 1,000 m | SI prefix: a thousand metres |
| Inch (in) | 0.0254 m | 1/36 yard, 25.4 mm exactly (1959) |
| Foot (ft) | 0.3048 m | 1/3 yard, 0.3048 m exactly (1959) |
| Yard (yd) | 0.9144 m | 0.9144 m exactly (1959) |
| Mile (mi) | 1,609.344 m | 1,760 yards, 1,609.344 m exactly |
| Nautical mile (nmi) | 1,852 m | 1,852 m exactly, by international agreement |
The metre itself is defined by light. The BIPM, which keeps the International System of Units, defines the metre by fixing the speed of light in vacuum at exactly 299,792,458 metres per second, so a metre is the distance light travels in 1/299,792,458 of a second. The inch, foot, yard and mile have been tied to the metre since the international yard and pound agreement of 1 July 1959, which set the yard at exactly 0.9144 m. That is why NIST’s table of conversion factors prints the inch (0.0254 m), the foot (0.3048 m), the yard and the mile in bold, its mark for an exact factor. The nautical mile, 1,852 m, is exact for a different reason: it was agreed as a round number of metres.
Because the factors are exact, some conversions end and some never do. Anything into metric from an inch-based unit always ends, since multiplying by 0.0254 can only add decimal places. Going the other way usually repeats: 1 cm is 50/127 of an inch, and 127 is a prime number, so the decimal 0.3937007874… never stops. The converter writes the exact digits in the working line and tells you whether the figure on the board was rounded.
Feet and inches: one length, two units
Feet and inches are one length written in two units, and they cause most of the mistakes people make with imperial lengths. The converter treats “feet and inches” as a unit of its own, so you can type a height or a room size the way it is written and get it back the same way.
| You type | It reads | In metres |
|---|---|---|
| 5′ 7″ | 5 ft 7 in | 1.7018 m |
| 5 ft 7 in | 5 ft 7 in | 1.7018 m |
| 5 7 | 5 ft 7 in | 1.7018 m |
| 5′ 7 1/2″ | 5 ft 7.5 in | 1.7145 m |
| 67″ | 67 in | 1.7018 m |
| 5.58 | 5.58 ft (decimal feet) | 1.700784 m |
The last row is the trap. 5.58 ft is five and fifty-eight hundredths of a foot, which is 5 ft 6.96 in, not 5 ft 58 in and not 5 ft 5.8 in. Surveyors, builders and spreadsheets use decimal feet; people talking about their height use feet and inches. When you convert into feet and inches, the converter rounds the total number of inches first and splits it into feet afterwards, so 71.97 inches comes out as 6 ft 0 in. Splitting first and rounding second is how some converters arrive at “5 ft 12 in”, which is not a length anyone writes.
On paper the marks are the prime (′) for feet and the double prime (″) for inches. A keyboard apostrophe and quotation mark stand in for them, and the converter accepts both, as well as the curly quotes a phone may substitute.
Metric, imperial and nautical: how the units step
Length units come in two families that meet at 25.4 mm. Inside each family the steps are fixed, and the metric family steps by ten, which is why a metric conversion is only ever a matter of moving the decimal point.
| Family | The steps | Used for |
|---|---|---|
| Metric (SI) | 10 mm = 1 cm; 100 cm = 1 m; 1,000 m = 1 km | Science, most of the world, all engineering drawings |
| US customary and imperial | 12 in = 1 ft; 3 ft = 1 yd; 1,760 yd = 1 mi | US daily life, UK road distances and heights |
| Nautical | 1 nautical mile = 1,852 m; a knot is 1 nautical mile an hour | Sea and air navigation |
| Typography | 72 points = 1 inch; 12 points = 1 pica | Font sizes and page layout |
The US and the UK share the same inch, foot, yard and mile since 1959, so there is no “UK inch” to choose. Volume is where the two differ (a UK pint is about a fifth bigger than a US pint), and the unit converter on the converters page labels those separately. For a single pair you convert often, the pages for centimetres to inches, millimetres to inches, feet to metres and kilometres to miles carry the tables and examples that belong to that direction, and the height converter handles centimetres and feet-and-inches for a person’s height.
What this converter does not do
This converts lengths, one dimension at a time. Areas and volumes change by the square and the cube of the factor: a square foot is 0.09290304 m², not 0.3048, so do not convert an area here. It does not convert speeds, though the mile and kilometre factor is the same one a speed uses. Entries are limited to a billion of the starting unit and 15 digits; negative lengths are refused.
| It does | It does not |
|---|---|
| Any of ten length units to any other, both ways | Convert areas, volumes or speeds |
| Feet and inches typed and returned as written | Guess which foot a pre-2023 survey used |
| Exact arithmetic, rounding only for display | Round inside the sum |
| Keep your entries in this browser | Send anything anywhere |
This converter or a one-formula one
What this page adds to a typical one-formula converter.
| This converter | A typical converter | |
|---|---|---|
| Units shown at once | All ten, from one entry | The pair you picked |
| Feet and inches | Typed and returned as written | Decimal feet only, or two boxes |
| Exact or rounded | Says which, with the exact digits | A rounded figure, unlabelled |
| Rounding carry | 71.97 in = 6 ft 0 in | Sometimes 5 ft 12 in |
| Fractions | 3/8, 5 3/8 and 5-3/8 accepted | Decimals only |
| Your entries leave the browser | Never | Varies |
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Frequently asked questions
How do you convert units of length?
Multiply by the size of the starting unit and divide by the size of the target unit, both in the same base unit. In metres, a yard is 0.9144 and a foot is 0.3048, so 10 yards in feet is 10 × 0.9144 ÷ 0.3048 = 30 feet. Within metric, move the decimal point: 1.5 m is 150 cm and 1,500 mm.
Is 1 inch exactly 2.54 cm?
Yes. Since the international yard and pound agreement of 1 July 1959 the yard has been exactly 0.9144 m, which makes the inch exactly 25.4 mm, or 2.54 cm. NIST lists it as an exact factor. Before 1959 the US and UK inches differed in the sixth or seventh significant figure, which is why the agreement was made.
How many feet are in a metre?
One metre is 3.2808398950… feet, which is 3 ft 3.37 in. The decimal never ends, because a foot is exactly 0.3048 m and 1 ÷ 0.3048 does not terminate. For most purposes 3.28 ft is close enough; for a building plan, use the converter and keep two decimal places of an inch.
How many metres are in a mile?
A mile is exactly 1,609.344 metres, which is 1,760 yards of 0.9144 m. A kilometre is therefore 0.6214 of a mile. The nautical mile used at sea and in the air is longer, 1,852 m, and the US survey mile, retired in 2023, was about 3.2 mm longer than the ordinary mile.
What is the difference between a mile and a nautical mile?
A statute mile is 1,609.344 m and a nautical mile is exactly 1,852 m, about 15% longer. The nautical mile began as one minute of latitude, which is why charts use it: a degree of latitude is about 60 nautical miles. Speeds at sea and in the air are in knots, nautical miles per hour.
How do I convert feet and inches to metres?
Turn the whole thing into inches first: 5 ft 7 in is 5 × 12 + 7 = 67 inches. Multiply by 0.0254 to get 1.7018 m. In the converter, choose feet and inches as the From unit and type 5' 7", 5 ft 7 in or 5 7, and it does both steps and shows them.
Why does my converter show 5 ft 12 in?
It split the length into feet before rounding the inches. 182.8 cm is 71.97 inches, which is 5 ft 11.97 in; rounding only the 11.97 gives 12, so the converter prints 5 ft 12 in. Round the total first: 71.97 rounds to 72 inches, which is 6 ft 0 in. This converter always rounds the total.
Can I convert square feet or cubic metres here?
No. Areas and volumes scale by the square and cube of the length factor, so a square foot is 0.09290304 m² and a cubic foot is 0.028316846592 m³. Using the plain length factor would be wrong by a factor of about three or ten. Use the area or volume part of the unit converter instead.
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