Convert m to dm metres ↔ decimetres Free Online Secure
Type a value in metres and read it in decimetres 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 dm (metres ↔ decimetres)
| m | dm |
|---|---|
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 5 | 50 |
| 10 | 100 |
| 20 | 200 |
| 50 | 500 |
| 100 | 1000 |
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.
Does anyone still use decimetres?
Rarely on its own: a decimetre is ten centimetres, and most people jump straight from centimetres to metres. It survives in school lessons and in one important place, the litre, which is exactly one cubic decimetre. That is why a litre of liquid fits in a cube ten centimetres on each side.
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.
Ten hand spans to the metre: when you need to convert m to dm
Almost nobody measures a room in decimetres, yet the unit sits quietly behind the metric system. The litre is a cubic decimetre, a cheese label may give a cake tin in decimetres, a Dutch carpenter speaks of a plank of "twelve decimeter", and school books in many countries keep the unit alive. When a figure in metres has to be compared with one in decimetres, you must convert m to dm. This page does the calculation as you type, so you can read the answer at once.
The rule is the simplest in the metric system: a metre has ten decimetres, so you multiply by ten, which moves the decimal point one place to the right. The sections below give the rule, worked examples, a short profile of each unit, a comparison, places where the conversion turns up, and the errors people make. Short as the topic is, a few practical details deserve space, especially for readers who meet the decimetre only on a worksheet.
How to convert m to dm: multiply by 10
The rule
One metre equals 10 decimetres. To convert m to dm, multiply the number of metres by 10 or move the decimal point one place to the right. 1 m is 10 dm, 2.5 m is 25 dm, 0.7 m is 7 dm, 12 m is 120 dm and 0.04 m is 0.4 dm. In the other direction, divide by 10.
Examples
A plank of 1.8 m is 18 dm. A room 4.2 m wide is 42 dm. A garden bed of 0.65 m is 6.5 dm. A swimming lane of 25 m is 250 dm. In each case the digits stay the same and only the decimal point moves.
A mental picture
To convert m to dm by eye, hold your hand out flat: the width from thumb tip to little finger tip is about a decimetre. Ten such hands laid in a row make a metre. If you want 3 m, think of thirty hands. This image makes it clear that decimetres outnumber metres by ten.
Fractions of a decimetre
Because a decimetre is 10 centimetres, 0.5 dm is 5 cm and 0.1 dm is 1 cm. A length such as 3.45 m is 34.5 dm, which equals 34 dm and 5 cm.
The metre
Base of the system
The metre is the SI base unit of length. It was proposed in 1791 as one ten-millionth of the quarter meridian and is now defined by the speed of light: the distance light travels in 1/299,792,458 of a second. The symbol is m.
Daily scale
A metre is about one long step, the width of a doorway plus a hand, or the height of a kitchen counter. Rooms, cables and tracks are described in metres.
The decimetre
One tenth of a metre
The decimetre is a tenth of a metre, ten centimetres. The prefix deci comes from the Latin for tenth. A cube with an edge of one decimetre holds exactly one litre, a fact that links length and volume.
Where it lives
In the Netherlands and Belgium the decimetre is part of everyday speech for craftspeople. Elsewhere it is mostly a classroom unit, though square and cubic decimetres appear in packaging, aquariums and cooking.
Metre and decimetre compared
A metre is ten times a decimetre, which is the smallest ratio between neighbouring metric units. Numbers in decimetres are ten times bigger than the same length in metres but still comfortable to read, which makes the unit handy for lengths between 10 cm and a few metres.
If your audience is used to centimetres, use them; if it follows a Dutch plan, use decimetres. Whichever you choose, label the unit and do not mix it with the other in one table.
Where you will need it
Litres and volumes
A tank 0.8 m long, 0.4 m wide and 0.5 m deep is 8 by 4 by 5 dm, so it holds 160 litres. Converting the sides first, using the “convert m to dm” calculation step, gives the volume in cubic decimetres, which equals litres. This is why aquarium dealers like the decimetre.
School exercises
Primary-school books often ask pupils to convert 3.4 m to decimetres. The answer, 34 dm, teaches the shift of the decimal point and prepares for centimetres and millimetres.
Dutch and Flemish plans
Plans from the Low Countries sometimes list lengths in decimetres. A plank of 24 dm is 2.4 m. A hedge of 36 dm is 3.6 m. If you buy materials abroad, ask whether the figures are in decimetres or centimetres.
Cooking and baking
Recipes from Central Europe sometimes give tin sizes in decimetres: a cake tin of 2.4 dm is 24 cm across, 0.24 m. Square decimetres appear in surface-area instructions for pastry dough.
Cubic decimetres and litres
One cube, one litre
A cube measuring 1 dm on each side has a volume of 1 dm³, which is 1 litre. A cube of 1 m on each side has 1,000 dm³, 1,000 litres, or 1 cubic metre. This is why a bath of 1.5 m by 0.7 m by 0.5 m, 15 by 7 by 5 dm, holds up to 525 litres.
Why it matters
Once your lengths are in decimetres, volumes come out in litres without any further conversion. For liquids, this is a major convenience. Convert all sides first, multiply, and read the litres.
Knitting and crafts
Gauge per decimetre
Knitting patterns give gauge in stitches per 10 cm, which is per decimetre. A gauge of 22 stitches per dm means a 0.5 m width needs 110 stitches. The conversion from metres to decimetres is a step in every garment calculation.
Fabric and ribbon
Ribbon is often sold by the metre but pieces are cut in decimetres: 7 dm for a bow, 15 dm for a gift. A reel of 10 m gives 14 bows.
Chess, boards and games
Board sizes
A tournament chessboard has squares of about 5.5 cm, a total of 0.44 m or 4.4 dm. A table-tennis table is 2.74 m by 1.525 m, 27.4 by 15.25 dm. Game designers use decimetres because the numbers are easy to draw.
Playgrounds
A hopscotch course of 3 m is 30 dm. A sandbox of 1.5 m by 1.5 m is 15 by 15 dm, which gives 2.25 m², 225 dm².
Lab measurements
Beakers and pipettes
Laboratory glassware is labelled in millilitres, but a lab bench might be 3.6 m long, 36 dm, and a fume hood 1.2 m wide, 12 dm. In chemistry classes the decimetre appears in concentration units, such as moles per dm³, which equals moles per litre.
Why dm³ appears
Moles per dm³ is an SI-friendly way to write moles per litre. It shows that the decimetre is far from dead in science.
Worked example: a window box
Dimensions and soil
A window box is 1.2 m long, 0.25 m wide and 0.2 m deep. Run each through the “convert m to dm” calculation step: 12 by 2.5 by 2 dm. The volume is 60 dm³, which is 60 litres of soil. A bag of compost holds 50 litres, so one bag and a bit more is needed. Two bags give a little spare.
Plants
With plants spaced 2 dm apart, the box takes 6 plants along its length. In decimetres the calculation is just 12 divided by 2.
Everyday references
Things about a decimetre
The width of a hand, a long pencil's stub, a mobile phone's length. A teaspoon of liquid is nothing next to a litre in a cube of 1 dm. Use these references to check your answers.
Things about a metre
A guitar, a baseball bat, the span from your nose to fingertip with your arm outstretched. Matching the references with the numbers improves your feel for the unit.
Measuring a classroom, step by step
Equipment and plan
Give each group a metre stick marked in decimetres and a sheet of paper. They measure the width of the room, the length of the board and the height of the door. Suppose the room is 7.2 m wide, the board 3.6 m and the door 2.05 m. Each group writes the figures in metres, runs a “convert m to dm” calculation on them and writes them again in decimetres: 72, 36 and 20.5.
Discussing the results
The class compares: the room is twice as wide as the board, 72 against 36. The door is a little over a quarter of the room width. The decimetre figures make these comparisons easy because the numbers are whole. Ask which unit helps most and why; most students choose decimetres or centimetres over metres with decimals.
Mixing the metric ladder in one task
A shelf project
A shelf is 1.35 m long, 22 cm deep and 18 mm thick. To describe it in one unit, convert: 13.5 dm long, 2.2 dm deep, 0.18 dm thick. The volume of the board is 13.5 times 2.2 times 0.18, about 5.3 dm³, 5.3 litres of wood. This is why a decimetre is handy for woodwork: when all sides are in decimetres, a quick multiplication gives the volume in litres, a number you can compare with other materials.
The lesson
The decimetre is a bridge between metres and centimetres. When a problem involves length, area and volume together, it often gives the cleanest numbers. A shelf of 13.5 dm is easier to handle than 1.35 m or 135 cm in the volume formula.
Square decimetres
Area of small surfaces
A square metre is 100 square decimetres. A tile of 0.3 by 0.3 m, 3 by 3 dm, has 9 dm². A painting of 0.6 by 0.8 m has 48 dm². Square decimetres are a comfortable unit for craft work.
Be careful with squares
The conversion factor for area is 100, not 10. When you move from m² to dm², multiply by 100. Forgetting the square is the commonest error.
Children's heights and growth
Tracking growth
A toddler of 0.85 m is 8.5 dm tall. A teenager of 1.62 m is 16.2 dm. Growth of 0.06 m a year is 0.6 dm. Although doctors use centimetres, some school projects ask pupils to plot growth in decimetres.
Measuring with hands
A class can measure a classroom wall in hand spans and convert, taking a span as about 1 dm. A wall of 6.3 m would be about 63 spans. The exercise brings the decimetre into daily life.
Aquariums and terrariums
Capacity from dimensions
A terrarium 0.9 m by 0.45 m by 0.45 m is 9 by 4.5 by 4.5 dm, which holds 182 litres. Subtract the substrate and the effective water volume falls. Shopkeepers quote the capacity in litres, but the glass sizes in centimetres, so a quick convert m to dm lets you check the claim.
Stocking rules
A common rule gives one litre of water per centimetre of fish, so a 182-litre tank suits fish totalling about 180 cm. Check the result against species guides before you buy.
Spreadsheet formulas
Formula
To convert m to dm for a list, put metres in column A and enter =A2*10 in column B. Format with one decimal. To convert a column back, divide by 10. For areas, multiply by 100, and for volumes by 1000.
Labels
Put the unit in the column header: "length (m)" and "length (dm)". When a colleague opens the sheet, no one will wonder whether the figures are decimetres or centimetres.
Rounding
How many decimals
One decimal in decimetres is a centimetre; two decimals are a millimetre. A tape reading of 2.34 m is 23.4 dm. Writing 23.40 dm adds a trailing zero that suggests a millimetre of precision.
Order of magnitude
The answer in decimetres has one more digit than the whole part of the metre value. 4.7 m becomes 47 dm, two digits against one. That check catches the commonest slip.
History of the decimetre
A unit in the original plan
The French commission of the 1790s planned a complete decimal ladder: decametre, metre, decimetre, centimetre, millimetre. The decimetre was part of it and even had its own standard rods in early sets. Over time, daily life skipped it, but the litre kept it alive.
The litre's story
The litre was defined in 1795 as one cubic decimetre. After 1901 it was briefly slightly different, 1.000028 dm³, and since 1964 it is again exactly 1 dm³.
Teaching the ladder
A drawn ladder
To convert m to dm on a ladder, draw one with the rungs kilometre, hectometre, decametre, metre, decimetre, centimetre, millimetre. Moving down one rung multiplies by ten. From metre to decimetre you move one rung, so you multiply by ten once. Mark each rung with an example object.
Games
In pairs, one student names a length in metres, the other gives it in decimetres, and the first checks with this page. Turn it into a race for speed and accuracy.
Gardening and planting
Spacing in decimetres
Seed packets sometimes give spacing in decimetres: lettuce at 2.5 dm, tomatoes at 5 dm, beans at 1 dm. A bed of 3 m, 30 dm, holds 12 lettuces, 6 tomatoes or 30 beans along one row. Convert the bed first and then divide.
Paths and borders
A border of 0.6 m is 6 dm wide. A path of 1.2 m is 12 dm. Planning a garden on squared paper with one square per decimetre keeps the scale simple.
More values for convert m to dm
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 = 1 dm
- 0.5 m = 5 dm
- 3 m = 30 dm
- 4 m = 40 dm
- 7 m = 70 dm
- 15 m = 150 dm
- 20 m = 200 dm
- 75 m = 750 dm
- 200 m = 2,000 dm
- 500 m = 5,000 dm
- 2,000 m = 20,000 dm
- 10,000 m = 100,000 dm
Mistakes when you convert m to dm
Moving the point the wrong way
Decimetres are smaller, so the number grows. If 3.4 m becomes 0.34, you moved left.
Using 100 for lengths
That gives centimetres. For decimetres, multiply by 10 only.
Forgetting the square or cube
Areas use 100 and volumes 1,000. Do not apply the length factor to them.
Quick answers
How many decimetres in a metre?
Ten.
How do I convert m to dm?
Multiply by 10.
What is 3.4 m in decimetres?
34 dm.
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 nm, Convert m to cm, Convert cm to dm, Convert ft to dm, Convert dm to cm, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L. The reverse of this page is Convert dm to m.
In short, to convert m to dm multiply by ten, move the decimal point one place 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.