Convert m to mm metres ↔ millimetres Free Online Secure
Type a value in metres and read it in millimetres 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 m to mm (metres ↔ millimetres)
| m | mm |
|---|---|
| 1 | 1000 |
| 2 | 2000 |
| 3 | 3000 |
| 5 | 5000 |
| 10 | 10000 |
| 20 | 20000 |
| 50 | 50000 |
| 100 | 100000 |
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
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.
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.
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.
A thousand small steps to the metre: how to convert m to mm
The metre is the unit of rooms and roads; the millimetre is the unit of workshops, rainfall gauges and camera lenses. A drawing may give a wall as 4.2 m while the plasterboard you buy is 12.5 mm thick, and a CNC machine accepts only millimetres. Whenever one figure is in metres and the other in millimetres, you have to convert m to mm, and this page does it as you type. The answer appears as a whole number or with decimals, whichever the input demands.
The rule is a multiplication by 1,000, which moves the decimal point three places to the right. It is exact and simple, but the numbers become large quickly, and a missing zero is a thousand-fold error. The sections below set out the rule with examples, say a little about each unit, compare them, look at the places where the conversion turns up and list the mistakes to avoid.
How to convert m to mm: multiply by 1,000
The rule
One metre is 1,000 millimetres. To convert m to mm, multiply the number of metres by 1,000, or move the decimal point three places to the right. 1 m is 1,000 mm, 2.5 m is 2,500 mm, 0.75 m is 750 mm, 0.012 m is 12 mm and 12 m is 12,000 mm. In the other direction, divide by 1,000.
Examples
A doorway of 0.9 m is 900 mm wide. A ceiling 2.4 m high is 2,400 mm. A board of 3.6 m is 3,600 mm long. A thickness of 0.018 m is 18 mm. A pipe 0.0213 m across is 21.3 mm. The digits stay the same; only the position of the decimal point changes.
Mental method
For a mental convert m to mm, think of the digits after the decimal point in a three-digit group: 1.375 m is 1 m and 375 mm, so 1,375 mm. If the metre figure has two decimals, add a zero: 1.37 m is 1,370 mm. If it has one, add two zeros: 1.4 m is 1,400 mm.
Very small values
For values below a millimetre, the answer has a decimal: 0.0004 m is 0.4 mm. A hair of 0.00007 m is 0.07 mm. Do not drop the leading zero.
The metre
Base unit
The metre is the base unit of length in the International System. It has been defined since 1983 by the speed of light, and it is the natural unit for everything from a pen to a pitch.
Strengths and limits
Metres suit rooms, vehicles and sports tracks. For machine parts, camera sensors and rainfall, they would give numbers full of decimals, which is where millimetres take over.
The millimetre
A thousandth of a metre
The millimetre is a thousandth of a metre. The prefix milli means a thousandth. A pencil lead is about half a millimetre, a coin two, a credit card three-quarters. It is the standard unit of mechanical drawings across the world.
Why drawings use it
Whole millimetres describe most workshop dimensions without decimals, and tolerances can be written as small fractions of a millimetre. International standards for screws, bearings and tools are all in millimetres.
Metre and millimetre compared
A metre is a thousand millimetres. The same length produces a number a thousand times bigger in millimetres. Use metres for lengths above a metre or so and millimetres for anything below a few centimetres. For lengths in between, centimetres are common.
In technical drawings it is usual to state a single unit in the title block, often millimetres, and to omit the unit on each dimension. When you receive a drawing, read the note before taking any figure.
Where you will need it
Building and carpentry
Plasterboard comes in sheets of 1,200 by 2,400 mm, which is 1.2 by 2.4 m. A wall of 5.4 m is 5,400 mm, 4.5 sheets wide. Studs are set 600 mm, 0.6 m, apart. Carpenters measure in millimetres, but room dimensions are given in metres, so the “convert m to mm” calculation step is constant.
Rain and snow
Rainfall is measured in millimetres: 1 mm is one litre per square metre. A shower of 25 mm over a roof of 80 square metres delivers 2,000 litres. A rain barrel of 0.2 m depth fills by 200 mm. The conversion from the metre depth of a barrel to the millimetre depth of rain is routine for gardeners.
Cameras
Lens focal lengths are in millimetres: 24, 50, 85, 200. A 200 mm lens is 0.2 m long in focal length though the barrel is longer. Close focusing distances are in metres: 0.45 m is 450 mm, the minimum focus of many lenses.
Manufacturing
A machine part drawn as 0.145 m long is 145 mm. Tolerances are plus or minus 0.1 mm, which is 0.0001 m. Programmers type millimetres into the controller, so a quick conversion from the metre dimensions on a plan prevents wrong cuts.
Classroom practice
Typical exercises
Pupils convert 0.35 m to millimetres and get 350 mm. They convert 2.045 m to 2,045 mm. Teachers often add a trap, such as 0.0045 m, which is 4.5 mm. The pattern is always the same: move the decimal point three places.
Self-check
Divide your answer by 1,000. If you return to the original number of metres, you have converted correctly. This reverse check works for every metric conversion and takes seconds.
Spreadsheet use
Formula
To convert m to mm for a column, put metres in column A and enter =A2*1000 in column B. Format with no decimals for whole millimetres or one decimal for tenths. To go back, divide by 1000. A column of whole-number millimetres is easier to read than metres with three decimals.
Avoiding the trap
Make sure that numbers copied from other documents are numbers and not text. If a cell is left-aligned, it may be text and the formula will fail. Convert with the value function.
A mental trick for builders
Counting by 100
Remember that 0.1 m is 100 mm, 0.2 m is 200 mm and so on. For 1.25 m, think 1,000 plus 250. For 3.675 m, think 3,000 plus 675. The decimal digits are simply the millimetres. This is how carpenters read a tape without calculating.
Checking a plan
Run your eye down a list of dimensions in metres and check that no value has more than three decimals. More would suggest micrometres, which would be out of place in a building plan.
Industry and CNC
From design to machine
A designer sketches a part at 0.25 m wide and 0.4 m long. The CNC machine accepts only millimetres: 250 by 400. The designer must convert m to mm before sending the file. A mismatch can result in a part that is a thousand times too small or large, wasting material and time.
Software settings
CAD programs let you choose units for the drawing. Set them to millimetres at the start. When you import a file from another system, check the units in the import dialog.
Weather records
Rainfall in context
Bucharest receives about 580 mm of rain a year, 0.58 m. A heavy daily rainfall is 50 mm, 0.05 m. A record storm may bring 150 mm in a day. The totals are always given in millimetres because the figures are whole numbers and easy to compare.
Snow
Snow depth is measured in centimetres, but snow water equivalent is in millimetres. A fresh snow cover of 30 cm may hold 30 mm of water, 0.03 m.
A worked example: building a shelf
Plan and cuts
A shelf unit is 1.8 m tall and 0.9 m wide, with five shelves of 18 mm board. Run the “convert m to mm” calculation step on the main dimensions: 1,800 by 900 mm. The side panels are 1,800 mm long. The shelves are 900 minus twice 18, which is 864 mm wide. Five shelves need 4,320 mm of board, 4.32 m, plus allowance for the saw kerf of 3 mm per cut.
Check
Add the thicknesses: five shelves of 18 mm are 90 mm of the 1,800 mm height. The gaps between shelves are then 1,710 divided by six, 285 mm each. Convert the result to metres, 0.285 m, for a summary: clear height between shelves is 28.5 cm.
Final checks
Three questions
After the conversion, ask whether the answer has three more digits than the whole number of metres, whether it ends in zeros as expected and whether it matches a rough estimate. If so, it is right. A conversion error of a factor of ten or a hundred is often visible in the number of digits.
Keep the original
When you pass on a converted figure, include the original in brackets. This lets the next reader verify it and prevents errors from compounding.
Choosing between metres and millimetres in your own documents
A rule of thumb
If most of your numbers would have more than three decimals in metres, switch to millimetres. If they would run to five digits in millimetres, switch to metres. A cabinet maker will quote a door as 720 mm; a surveyor will quote a boundary as 41.5 m. Where both appear together, as on a building plan with window details, state the unit beside every figure and, after each “convert m to mm” calculation, keep the result in the unit your readers will use.
Consistency pays
A document in a single unit is easier to check than one that alternates. Convert everything once, at the start, and write the converted values into the plan. Anyone who later needs the original can find it in your notes.
Cooking and kitchen measures
Thickness in recipes
Pastry is rolled to 3 mm, pizza dough to 5 mm, biscuits to 6 mm. A kitchen worktop is 38 mm thick, a cutting board 20 mm. A pasta machine's settings run from 0.5 mm to 5 mm. In metres, a 3 mm pastry is 0.003 m, a number nobody uses in a kitchen.
Slicing
Vegetables are sliced to 2 mm for crisps and 10 mm for stews. A mandoline gives slices of 1.5 mm, 0.0015 m. Cooks use millimetres because the numbers are whole and the unit matches the size of the cut.
Gardening and growing
Seed depth and spacing
Fine seeds such as carrots are sown 5 mm deep; beans at 30 mm. A plant growing 4 mm a day grows 0.12 m in a month. Growth data from sensors are usually recorded in millimetres per day.
Rain gauges
A garden rain gauge reads in millimetres. A week with 18 mm of rain delivers 18 litres per square metre. If your watering can adds 5 litres to a bed of 2 square metres, that is 2.5 mm. Compare that with the rain to decide whether to water.
Laboratory and science
Precision work
Laboratory lengths range from metres of benchtop to millimetres of apparatus. A burette of 0.5 m has a scale in 0.1 ml divisions; a Petri dish is 90 mm across; a microscope slide 76 by 26 mm. All of these are quoted in millimetres.
Converting for formulas
Many physics formulas require metres, so a radius of 25 mm must become 0.025 m before it is used. Forgetting the step gives an error of a factor of 1,000, or 1,000,000 in the area.
History of the millimetre
Part of the first metric system
The millimetre was part of the original metric system of the 1790s. Craftsmen soon adopted it because it matched the smallest division they could work with. It took more than a century to become universal in engineering drawings.
Standardisation
The ISO standards of the 20th century fixed millimetres as the default for mechanical drawing. Except for a few industries, such as aerospace in the United States, the millimetre now dominates technical work.
Rounding and tolerance
How many decimals
A measurement of 2.4 m to the nearest centimetre is 2,400 mm, but if the real accuracy is 5 mm, say 2,400 plus or minus 5. Writing 2,400.0 mm suggests a tenth of a millimetre. Keep the digits that your measurement justifies.
Cumulative error
Ten pieces of 0.325 m each are 3.25 m, or 3,250 mm. If each piece is cut with an error of 1 mm, the total can be 10 mm out. Cut to a story rod rather than adding up measurements.
Insects, hair and small things
Everyday smallness
A house fly is 7 mm long, 0.007 m. An ant is 3 mm. A grain of rice is 6 mm. A human hair is 0.07 mm, 0.00007 m. A sheet of paper is 0.1 mm. These sizes make the millimetre feel real.
Putting them in metres
A hair in metres is 7 times ten to the minus five, an awkward figure. It shows why the millimetre is the right unit for small things.
Music and instruments
Strings and frets
A guitar's scale length is about 650 mm, 0.65 m. Strings range from 0.25 mm to 1.2 mm in diameter. The frets are spaced by a formula: the first fret is 36.5 mm from the nut. A luthier works in millimetres and converts the length of the wood from metres.
Pianos and wind instruments
A piano string is up to 2 m, 2,000 mm. A flute is 670 mm long, 0.67 m, with holes of 5 to 13 mm. The conversion is often needed by instrument makers reading old plans in metres.
Language and symbols
Milli and metre
Milli comes from the Latin for a thousand, so a millimetre is a thousandth of a metre. In most languages the word is nearly the same: millimeter, millimètre, millimetro, milímetro. The symbol is mm, with no full stop.
Writing numbers
Put a space between the number and the unit and use thousands separators for long figures: 2,400 mm. In some languages a point is used instead of a comma; follow the convention of your reader.
More values for convert m to mm
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 m = 100 mm
- 0.5 m = 500 mm
- 3 m = 3,000 mm
- 4 m = 4,000 mm
- 7 m = 7,000 mm
- 15 m = 15,000 mm
- 20 m = 20,000 mm
- 75 m = 75,000 mm
- 200 m = 200,000 mm
- 500 m = 500,000 mm
- 2,000 m = 2,000,000 mm
- 10,000 m = 10,000,000 mm
Mistakes when you convert m to mm
Moving the point the wrong way
Millimetres are smaller, so the number grows. If 0.35 m becomes 0.00035, you moved left.
Two places instead of three
That gives centimetres. For millimetres move three places.
Losing a leading zero
0.045 m is 45 mm, not 4.5 mm. Count the places carefully.
Quick answers
How many millimetres in a metre?
One thousand.
How do I convert m to mm?
Multiply by 1,000.
What is 0.35 m in millimetres?
350 mm.
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 m to yd, Convert m to cm, Convert cm to mm, Convert µm to mm, Convert mm to in, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L. The reverse of this page is Convert mm to m.
In short, to convert m to mm multiply by a thousand, move the decimal point three places to the right and keep only the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.