Convert mm to m millimetres ↔ metres Free Online Secure
Type a value in millimetres and read it in metres at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert mm to m (millimetres ↔ metres)
| mm | m |
|---|---|
| 1 | 0.001 |
| 2 | 0.002 |
| 3 | 0.003 |
| 5 | 0.005 |
| 10 | 0.01 |
| 20 | 0.02 |
| 50 | 0.05 |
| 100 | 0.1 |
Where these units come from
The metre was first defined in 1793 as a ten-millionth of the distance from the equator to the North Pole — a definition nobody could check without surveying a quarter of the planet. It has been redefined four times since, each time to something steadier: a platinum bar, then a prototype kept in Paris, then a wavelength of krypton light, and since 1983 the distance light travels in vacuum in 1/299,792,458 of a second. The inch stopped being a separate thing in 1959, when six countries agreed to define it as exactly 25.4 mm. That agreement is why every conversion on this page between a metric and an imperial length is exact rather than measured: both sides now descend from the same definition.
Where you meet them
Millimetres are the working unit of engineering drawings and of anything made in a workshop; centimetres belong to tailoring, furniture and school rulers; metres to rooms, fabric and running tracks. Feet and inches survive in aviation altitudes worldwide, in American and British construction, and in the diagonal of every screen you have ever bought. Nautical miles are not a quaint survival — one is a minute of latitude, which is why ships and aircraft still navigate in them.
Questions people ask
Why do engineering drawings use millimetres?
Because a millimetre is small enough that nearly every dimension of a manufactured part is a whole number or a short decimal, which leaves no room for the arithmetic mistakes that fractions invite. Drawings in millimetres state the unit once and then drop it, and tolerances are written the same way, in hundredths or thousandths of a millimetre.
How is the metre defined today?
As the distance light travels in a vacuum in 1/299,792,458 of a second. The definition has been in place since 1983 and ties the metre to the speed of light, which is itself fixed at exactly 299,792,458 metres per second. The old platinum bar in Paris no longer defines anything.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
From the drawing board to the building site: how to convert mm to m
Architects and engineers draw in millimetres: a wall of 4,200, a window of 1,350, a ceiling of 2,700. Buyers, builders and buyers' families talk in metres: a room four metres wide, a ceiling two and three quarters. Moving from the drawing to the conversation is one of the most frequent conversions in the building trades, and the one that most often goes wrong when someone misplaces a decimal point. Whenever a dimension in millimetres must be read as a length in metres, you have to convert mm to m. This page does it as you type.
The rule is a division by one thousand, which moves the decimal point three places to the left. It is exact and quick, but it is easy to make a mistake with long numbers. The sections below give the rule with examples, short portraits of the two units, a comparison, a tour of the places where the conversion appears and a list of the mistakes people most often make.
How to convert mm to m: divide by 1,000
The rule
One metre is 1,000 millimetres. To convert mm to m, divide the number of millimetres by 1,000 or move the decimal point three places to the left. 1,000 mm is 1 m, 2,700 mm is 2.7 m, 450 mm is 0.45 m, 75 mm is 0.075 m and 12,500 mm is 12.5 m. In the other direction, multiply by 1,000.
Examples
A wall of 4,200 mm is 4.2 m. A ceiling height of 2,400 mm is 2.4 m. A door 2,040 mm high is 2.04 m. A bridge of 36,000 mm is 36 m. A pipe of 18 mm is 0.018 m. In each case the digits are the same and the decimal point moves three places.
Mental method
For a mental convert mm to m, look at the last three digits: they are the millimetres left after the whole metres. 2,740 mm is 2 m and 740 mm, so 2.74 m. For numbers under a thousand, the answer begins with 0.: 850 mm is 0.85 m, 85 mm is 0.085 m.
Large numbers
Drawings of big structures give dimensions such as 124,500 mm. Place a mark between the thousands: 124,500 becomes 124 m and 500 mm, 124.5 m. The comma in the original is the guide.
The millimetre
The drawing unit
The millimetre is a thousandth of a metre. It is the standard on technical drawings, because every dimension is a whole number, and because it is the unit of the tolerances that decide whether parts fit. The symbol is mm.
Everyday objects
A coin is 2 mm thick, a credit card 0.76 mm, a pencil lead 0.5 mm. A phone is 8 mm. A plasterboard is 12.5 mm. These are the sizes that make millimetres natural.
The metre
The base unit
The metre is the SI base unit of length, defined since 1983 from the speed of light. It is the unit of rooms, vehicles, tracks and sports fields, and the natural unit of everything bigger than a hand.
In buildings
Floor plans give room sizes in metres, because people think in them. A bedroom of 3.5 by 4 m is easier to picture than 3,500 by 4,000 mm. Heights, such as a ceiling of 2.6 m, are always said in metres.
Millimetre and metre compared
A metre is a thousand millimetres. The same length gives a number a thousand times smaller in metres. Use metres for anything over a metre or so and millimetres for anything where a millimetre matters.
In construction it is common to use both on one drawing: overall dimensions in metres, details in millimetres. State which is which in the title block, and never mix them in one chain of dimensions.
Where you will need it
Building plans
An architect gives a living room as 5,400 by 3,800 mm. The estate agent says 5.4 by 3.8 metres. The area is 20.5 square metres. A buyer who compares two flats must convert mm to m for every room before adding. Ceiling height matters too: 2,400 mm is a low ceiling, 2,700 a comfortable one, 3,000 spacious.
Cars and vehicles
A car's wheelbase is 2,700 mm, 2.7 m, its length 4,500 mm, 4.5 m, its width 1,800 mm, 1.8 m. A garage door of 2,400 mm is 2.4 m wide, enough for a car with doors closed but tight for opening. Parking spaces are 2,500 by 5,000 mm.
Machines and industry
A lathe of 1,500 mm bed length is 1.5 m. A conveyor of 24,000 mm is 24 m. Factory floor plans show machines in millimetres and aisles in metres. A forklift needs an aisle of 3,200 mm, 3.2 m.
Measuring tools
A laser distance meter shows 3,627 mm or 3.627 m. Tape measures show both centimetres and millimetres; a long tape of 5 m has 5,000 mm marked in tens. Digital instruments offer a button for the unit.
Reading architectural drawings
Conventions
Architectural drawings use millimetres without the unit, so a 4200 is 4,200 mm. The title block states: "all dimensions in mm". Levels, such as floor heights above a datum, are in metres: +3.150. This mix catches newcomers, who must convert mm to m for dimensions but not for levels.
Checking sums
Add a string of dimensions: 1,200 plus 900 plus 1,500 plus 600 is 4,200 mm, 4.2 m. The sum must match the overall dimension on the plan. Many errors are found by adding the string.
Language and symbols
Symbols
The symbols mm and m are written in lower case, without a full stop. Do not add s for plurals. A space goes between the number and the unit: 2,700 mm. Use a thin space or comma as a thousands separator, and be consistent.
Words
Milli, from Latin mille, thousand. Metre, from Greek metron, measure. The millimetre is thus a thousandth of a measure, and the name is similar in many languages: Millimeter, millimètre, millimetro.
A worked example: a kitchen
From drawing to order
A kitchen drawing shows a wall of 3,600 mm with units of 600 mm, a corner of 900 mm and a tall unit of 600 mm. The units add to 3,000 mm, leaving 600 mm for a gap. To convert mm to m for the buyer: wall 3.6 m, units 3.0 m, gap 0.6 m. The worktop must be 3,600 mm long, but supplier lengths come in 3.0 and 4.1 m, so order 4.1 m and cut.
Checking
Multiply 3.6 by 1,000 to return to 3,600. Check the sum of the units: 600 plus 600 plus 600 plus 600 plus 600 equals 3,000. All consistent.
Final checks
Round trip
Multiply your answer by 1,000. If you return to the millimetres you started with, the conversion is right. If you get 100 times too much or too little, you moved the point two places.
Notes
Write both the millimetre and metre figures in your notes. A later reader can check them in seconds.
Stairs, risers and going
The rule of the staircase
A comfortable stair has a riser of 150 to 180 mm and a going of 250 to 300 mm. A storey of 2,800 mm needs 16 risers of 175 mm. The total run of 15 goings of 280 mm is 4,200 mm, 4.2 m. The drawing gives these dimensions in millimetres; the owner wants to know how much space the stair takes, so run the “convert mm to m” calculation step: 4.2 m of floor and 2.8 m of height.
Headroom
Building codes require a headroom of at least 2,000 mm, 2 m, above the stair. A stair that climbs 2,800 mm through a opening in the ceiling needs an opening of at least 4,200 mm, 4.2 m, to keep the headroom, otherwise a person climbing hits the ceiling at the top.
Fences, decking and landscaping
Board and post sizes
A deck board is 28 by 140 mm with a gap of 5 mm. A post is 100 by 100 mm and 2,400 mm long, of which 600 mm goes in the ground. A fence panel is 1,800 mm high and 1,830 mm wide. Landscape plans give these in millimetres, while a customer talks about a fence of 1.8 m height. The conversion keeps the two conversations in line.
Counting boards
A deck 3,000 mm wide takes 3,000 divided by 145, which is 20.7, so 21 boards across. Round up to 21, then add 5 per cent for cuts. Express the finished area in square metres: 3 m by 4.2 m is 12.6 m².
Roads, lanes and clearances
Standard widths
A road lane is 3,000 to 3,750 mm, 3 to 3.75 m. A cycle path is 2,000 mm, 2 m. A footpath is 1,500 mm, 1.5 m. The clearance under a bridge is 4,500 mm, 4.5 m, so that lorries of 4,000 mm height can pass. Road drawings use millimetres for details and metres for the overall layout.
Reading a cross-section
A cross-section shows a carriageway of 7,300 mm, a verge of 2,500 mm and a ditch of 1,200 mm. The total width is 11,000 mm, 11 m. A designer states the width of the road reserve in metres, so someone must convert mm to m for each element before adding.
Tape measures and laser meters
Reading the instrument
On a standard tape the numbered marks are centimetres; the millimetres are the small marks. A reading of 137 cm and 4 small marks is 1,374 mm, 1.374 m. A laser meter shows 1.374 on its screen with the unit m, or 1374 with mm, depending on the setting.
Setting the unit
Choose the unit before you measure. If the instrument is in metres and your drawing in millimetres, write down the value as the instrument shows it and convert later, not in your head on site.
Tolerances in construction
How much is acceptable
A wall may be out of plumb by 5 mm in 2.4 m, which is 0.2 per cent. A floor may be flat within 3 mm under a 2 m straightedge. A tile joint has a tolerance of 1 mm. In metres these tolerances are 0.005, 0.003 and 0.001, numbers that nobody uses, which is why tolerances are always in millimetres.
Cumulative error
Ten pieces of 600 mm cut each 1 mm too long add up to 10 mm, 0.01 m, too much. Mark the cuts from one reference rather than adding measurements.
Rain and reservoirs
From millimetres to metres
Annual rainfall of 650 mm is 0.65 m. Over an area of 1 square kilometre, 1,000,000 square metres, that is 650,000 cubic metres of water. A reservoir 2 m deep and 1 km long and 100 m wide holds 200,000 cubic metres, about a third of a year's rain on the same area.
Why metres here
Volumes in cubic metres need depth in metres. A rain gauge reads millimetres; engineers then convert mm to m before multiplying by area.
Wire, rope and cable
Lengths on reels
Cable is sold by the metre but cut by the millimetre on a production line. A reel of 100,000 mm is 100 m. A cable assembly of 1,250 mm is 1.25 m. A harness of 2,300 mm is 2.3 m. Electricians quote sizes in metres to clients and in millimetres to the workshop.
Allowances
Add 5 per cent for slack and connectors. A run of 8,400 mm, 8.4 m, becomes 8.82 m, so order 9 m.
Spreadsheet formulas
Formula
To convert mm to m for a column, put millimetres in column A and enter =A2/1000 in column B. Format with three decimals for millimetre precision or two for centimetre precision. To reverse, multiply by 1000. For a string of dimensions, sum the column first and convert once.
Check values
Enter 1000: result 1. Enter 2700: 2.7. Enter 75: 0.075. If you see 2.7E+00, the cell is in scientific format; change it to number.
Rounding
Match the precision
A length of 2,743 mm to the nearest millimetre is 2.743 m. If you give 2.74 m, you round to the nearest centimetre. A drawing for a builder usually keeps millimetres; a description for a buyer rounds to the centimetre or even the decimetre.
Rounding sums
Do not round before adding. Four lengths of 1.2345 m each rounded to 1.23 add to 4.92 m, whereas the true sum is 4.938 m. Convert after summing.
Teaching the shift
A three-column table
To teach the “convert mm to m” calculation, draw a table with the columns millimetre, centimetre, metre. Enter 2,700 mm, 270 cm, 2.7 m. Students see that each step is a division by ten (to centimetres) or by a hundred (to metres). The three-step table is the same as the metric ladder.
Practice
Give students ten lengths from a building plan in millimetres and ask them to convert each to metres. Check with this page. The most common error is moving the point two places.
History of the drawing standard
From local units to millimetres
Before the 20th century, drawings used feet, inches, ells and local measures. When industry demanded interchangeable parts, standards bodies chose the millimetre as the universal unit for mechanical drawings. By the 1950s most European drawings were in millimetres, and the practice spread around the world.
Why not metres
Metres would force decimals on nearly every dimension. Millimetres keep them whole, which reduces errors in transcription and speeds up reading.
More values for convert mm to m
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 mm = 0.0001 m
- 0.5 mm = 0.0005 m
- 3 mm = 0.003 m
- 4 mm = 0.004 m
- 7 mm = 0.007 m
- 15 mm = 0.015 m
- 20 mm = 0.02 m
- 75 mm = 0.075 m
- 200 mm = 0.2 m
- 500 mm = 0.5 m
- 2,000 mm = 2 m
- 10,000 mm = 10 m
Mistakes when you convert mm to m
Moving two places
That gives centimetres. For metres, three places.
Moving the wrong way
The metre is the larger unit, so the number gets smaller. If 2,700 mm becomes 2,700,000, you moved right.
Dropping the leading zero
85 mm is 0.085 m, not 0.85 m.
Quick answers
How many metres in a millimetre?
0.001.
How do I convert mm to m?
Divide by 1,000.
What is 2,700 mm in metres?
2.7 m.
Is the conversion exact?
Yes, exact.
Does my number leave my device?
No. The calculation runs in your browser.
Related pages and a last word
If you work with lengths, these conversions are close at hand: Convert mm to in, Convert mm to cm, Convert nm to m, Convert yd to m, Convert m to yd, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L. The reverse of this page is Convert m to mm.
In short, to convert mm to m divide by a thousand, move the decimal point three places to the left and keep only the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.