Convert cm to dm centimetres ↔ decimetres Free Online Secure
Type a value in centimetres 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 cm to dm (centimetres ↔ decimetres)
| cm | dm |
|---|---|
| 1 | 0.1 |
| 2 | 0.2 |
| 3 | 0.3 |
| 5 | 0.5 |
| 10 | 1 |
| 20 | 2 |
| 50 | 5 |
| 100 | 10 |
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
Where is the centimetre used in everyday life?
For anything a person measures against their own body: height, clothing sizes, the length of a sleeve, the width of a shelf, the dimensions of a parcel. A centimetre is roughly the width of a fingernail, which makes it easy to picture. It is large enough to avoid long strings of digits and small enough that you rarely need a decimal.
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.
The forgotten step between centimetre and metre: why you might convert cm to dm
Most people know centimetres and metres by heart, and many have never used the decimetre at all. Yet it sits exactly between them: ten centimetres make a decimetre, and ten decimetres make a metre. In some countries, notably the Netherlands, Belgium and parts of Eastern Europe, the decimetre appears in school books, in the shop (a "5 dm" ribbon), in the garden and above all in a famous equation of the metric system: a cube one decimetre on a side holds exactly one litre. When a figure in centimetres has to be read in decimetres, you have to convert cm to dm. This page does it instantly: type a length in centimetres and read it in decimetres.
The arithmetic could hardly be simpler. A decimetre is ten centimetres, so you move the decimal point one place to the left. What makes the page useful is not the sum but the confidence: the result is exact, there is no rounding, and the explanations below tell you where the decimetre comes from, where it is still used and how to avoid the few slips that exist in so easy a conversion.
One step of the decimal ladder
The rule
One centimetre is 0.1 decimetre, and one decimetre is 10 centimetres. To convert cm to dm, divide the number by ten, which means moving the decimal point one place to the left. 75 cm is 7.5 dm, 8 cm is 0.8 dm, 120 cm is 12 dm and 3.5 cm is 0.35 dm. There are no exceptions, no rounding and no special cases.
Four small examples
A school ruler of 30 cm is 3 dm. A child's height of 118 cm is 11.8 dm. A shelf 62 cm wide is 6.2 dm. A fingernail of 1.2 cm is 0.12 dm. Because the factor is a power of ten, the answer has exactly the same digits as the question, only the decimal point has moved.
In your head
Cover the last digit with your thumb: 340 cm becomes 34 dm. If the number has a decimal part, shift the point instead: 34.5 cm becomes 3.45 dm. Check that the answer is ten times smaller than the starting number; if it is not, you moved the point the wrong way.
Writing the result
Keep the same number of significant figures that you started with. A length measured as 12.5 cm is 1.25 dm, not 1.2500 dm. Trailing zeros suggest precision that the measurement may not have.
The centimetre
A hundredth of a metre
The centimetre is the everyday unit of the metric world for objects between a coin and a wardrobe. Rulers, tailors' tapes, baby growth charts and kitchen cabinets use it, and it is small enough to avoid decimals for most household lengths. Its prefix, centi, means a hundredth, from the Latin centum, one hundred.
In use
Height charts, clothes patterns, shoe length, picture frames and fabric widths are all given in centimetres. Its symbol is cm, and two centimetres squared is written cm², not 2 cm.
The decimetre
A tenth of a metre
The decimetre is a tenth of a metre, about the width of a hand, from the Latin decimus, tenth. It was among the original units when the metric system was designed in the 1790s, and it was used to define the litre: a cube with edges of one decimetre contains a litre of water, which weighs a kilogram. That link between length, volume and mass is the most elegant feature of the system.
In use
In the Netherlands and Belgium the decimetre is a school staple, and Dutch carpenters and gardeners speak of "dm" in speech. Elsewhere it turns up in the area unit dm², in the volume unit dm³ and in map making. The symbol is dm. When you convert cm to dm, you are stepping between the two units that built the litre.
Centimetre and decimetre compared
A decimetre is ten times a centimetre, so a length in decimetres has one tenth of the digits. 100 cm is 10 dm; 1 dm is 10 cm. A rule of thumb: the decimetre is about a hand's width and the centimetre about a finger's.
For most purposes the centimetre is more convenient, because it gives whole numbers for small objects. The decimetre is the better unit when the quantity is part of a litre calculation or when a textbook demands it. If you are writing for a reader, state which unit you mean, because many people will read dm as decimetre and some as something else.
When a conversion from cm to dm is needed
At school
Children in many countries learn the metric ladder with centimetres, decimetres and metres, and homework often asks them to convert cm to dm or the reverse. A typical exercise: a ribbon is 85 cm long; how many decimetres is it? Answer: 8.5 dm. Teachers use the decimetre to show that each step is a factor of ten, and a good trick is to draw the ladder with millimetre, centimetre, decimetre and metre as rungs.
Volume and litres
Because one litre is one cubic decimetre, a container measured in centimetres has to be changed to decimetres before its capacity can be read in litres. A tank 40 cm × 30 cm × 25 cm is 4 dm × 3 dm × 2.5 dm, which gives 30 dm³, or 30 litres. Aquarium owners, plumbers and chefs do this sum without thinking, and it is the neatest reason to convert cm to dm.
Crafts and workshops
Knitters, quilters and dressmakers who follow Dutch or Belgian patterns meet decimetres in the margins. A sleeve length of 56 cm is 5.6 dm; a pattern block of 25 cm is 2.5 dm. Model makers and woodworkers use the unit when they want to read a plan in one shot, because most hobby parts are between 1 and 20 dm.
Maps and surveying
Older maps and some architectural drawings use decimetre grids. A map at 1:1000 shows 1 dm as 100 m on the ground. When you read an old plan, check the scale and the unit in the corner, and convert cm to dm before you rely on a printed distance.
How the decimal ladder was built
The 1790s idea
When France's scientists designed the metric system, they wanted every unit to be related to the next by a factor of ten, so that arithmetic would be as easy as shifting a decimal point. They defined the metre first, then derived the litre, the gram and the are from it. Prefixes in Latin and Greek, deci, centi, milli, deca, hecto, kilo, were applied across all units. The system spread because it removed the confusion of local feet and pounds.
The prefix family
The prefixes now cover sixty orders of magnitude, from quecto, one nonillionth, to quetta, one nonillion. Deci is rarely used outside the decibel, the decilitre and the decimetre; most users jump from metre to centimetre and from centimetre to millimetre. That is why the decimetre feels like a forgotten rung. In science, standards bodies discourage deci and centi in favour of powers of three, but everyday life ignores the advice.
Prefixes in the kitchen
Decilitres appear in Scandinavian recipes, where a "dl" is a standard unit of cooking, equal to 100 millilitres. A Swedish recipe may call for 3 dl of flour. The same logic applies to length: a decimetre is a hundred millimetres.
When the decimetre makes life easier
Rough estimates
Decimetres are excellent for quick estimates by hand and eye. A hand span is about two decimetres, a shoe about three, a cat about four and a baby about five. If you must convert cm to dm for such objects, the answer is a small number you can hold in your head, which is easier than juggling three-digit centimetre figures. Teachers use the unit for this reason, and so do people who plan furniture on the back of an envelope.
Planning rooms
A small room of 300 cm by 250 cm is 30 dm by 25 dm; the area is 750 dm², which is 7.5 m². The numbers are shorter than in centimetres and easier to scale than in metres with decimals. For quick budgeting of paint, tiles or flooring, a decimetre grid is a handy intermediate.
Measurement habits
Choosing the unit that fits
A good unit gives numbers between 1 and 1,000. For a pencil, centimetres give 19 cm; decimetres give 1.9 dm, which is clumsier. For a room, metres are best. The decimetre gives sensible numbers for objects between 10 cm and 1 m long, such as a book (2.4 dm), a shoe (3 dm), a bread loaf (4 dm). If you must convert cm to dm in a document, mention the original unit in brackets so the reader can check.
Tools
Most rulers and tapes do not mark decimetres, only centimetres and millimetres. To measure in decimetres, count the long marks every ten centimetres. A folding carpenter's rule often has each decimetre in a different colour. Digital callipers can switch units, and a laser measure may display in decimetres in some regions.
Accuracy
Accuracy depends on the instrument, not on the unit. A measurement of 25 cm made with a tape accurate to 1 mm is really 25.0 cm, or 2.50 dm. Report the digits you can trust.
Common mistakes
Moving the point the wrong way
The most frequent slip is to move the decimal point to the right when going from smaller units to larger ones. Remember that the unit gets bigger, so the number gets smaller. Ask whether the answer is a tenth of the starting figure.
Mixing dm and cm in one sum
Do not add 3 dm and 25 cm directly. Convert one to the other first: 25 cm is 2.5 dm, so the total is 5.5 dm, or 55 cm. In a long list of lengths, write the unit beside every figure to avoid slips.
Quick references
A small table
1 cm = 0.1 dm; 5 cm = 0.5 dm; 10 cm = 1 dm; 25 cm = 2.5 dm; 50 cm = 5 dm; 100 cm = 10 dm; 150 cm = 15 dm. Learn the pattern and you will never need to convert cm to dm with a calculator.
Body anchors
A hand span is about 2 dm, a foot about 2.5 to 3 dm, a forearm about 3 to 4 dm and an arm span about 17 dm. These anchors make it easier to judge a length by eye and to check that a result is plausible.
The litre, the kilogram and the decimetre
A cube of water
The most beautiful consequence of the decimal ladder is that three different quantities are tied together. A cube with edges of one decimetre, that is ten centimetres, has a volume of one cubic decimetre, which is one litre. Fill it with pure water at its densest, around four degrees Celsius, and it weighs one kilogram. Length, capacity and mass thus come from a single unit, a link that the designers of the system built on purpose. Anyone who needs to convert cm to dm to find a volume in litres is walking the same path.
A worked example
Suppose you have a plastic box measuring 35 cm by 20 cm by 15 cm and want to know how many litres it holds. First change each side to decimetres: 3.5 dm, 2 dm and 1.5 dm. Multiply them: 3.5 × 2 × 1.5 = 10.5 dm³, which is 10.5 litres. Had you multiplied centimetres, you would have 10,500 cm³ and had to divide by a thousand; the decimetre route saves a step and a source of error.
Everyday containers
A shoebox is about 3 dm × 2 dm × 1.2 dm, or 7 litres. A standard bucket is about 3 dm across and 3 dm high, roughly 12 litres. A bath is around 150 litres. These sizes help you check whether a conversion result is sensible and are a good way to teach children what a litre looks like.
Where the decimetre lives today
Dutch and Belgian habits
In Dutch-speaking countries the word decimeter is part of daily speech. A tailor may speak of a skirt of "vier decimeter", a carpenter of a plank of "drie decimeter", and children measure the length of a classroom desk in decimetres before they move on to metres. In these places the ladder of millimetre, centimetre, decimetre, metre is taught as a single, linked system, and a pupil who has to convert cm to dm knows it as moving one place on the ladder.
Elsewhere
In English-speaking countries the decimetre is nearly absent from everyday talk. It appears in science lessons, in a few trade catalogues and in the units of area and volume, dm² and dm³. In French, the word décimètre is often used for a ruler of that length, a "double décimètre" being a ruler of twenty centimetres. Knowing that the unit exists will help you read foreign recipes, plans and textbooks without confusion.
A tip for translators
If you translate a text that mentions decimetres into a language where the unit is unknown, convert it to centimetres in the translation and keep the original in brackets. The reader will understand at once, and a technical reviewer can trace the figure back.
More values for convert cm 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 cm = 0.01 dm
- 0.5 cm = 0.05 dm
- 3 cm = 0.3 dm
- 4 cm = 0.4 dm
- 7 cm = 0.7 dm
- 15 cm = 1.5 dm
- 20 cm = 2 dm
- 75 cm = 7.5 dm
- 200 cm = 20 dm
- 500 cm = 50 dm
- 2,000 cm = 200 dm
- 10,000 cm = 1,000 dm
Slips to avoid when you convert cm to dm
Multiplying by ten
Going from centimetres to decimetres means a smaller number. Multiplying by ten gives the wrong answer, a hundred times too big when the correct step is a tenth.
Confusing dm with dm²
One decimetre is a length; a square decimetre is an area of 100 cm², and a cubic decimetre a volume of 1,000 cm³. If you are converting areas or volumes, use the right page.
Dropping the unit
Always write the unit next to the number. "12" could be 12 cm or 12 dm, a factor of ten apart.
Quick answers
How many centimetres are in a decimetre?
Ten.
How do I convert cm to dm?
Divide by ten, or move the decimal point one place to the left.
What is 50 cm in dm?
5 dm.
Is the conversion exact?
Yes, it is exact, because both units are defined from the metre by powers of ten.
Is my number sent anywhere?
No. The calculation runs in your browser and nothing is uploaded.
Related pages and a last word
If you work with small lengths regularly, these conversions are close by: Convert cm to in, Convert cm to mm, Convert in to dm, Convert m to dm, Convert dm 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 dm to cm.
In short, to convert cm to dm divide by ten, check that the answer is smaller than the starting figure and keep the digits that your measurement supports. Your number stays on your device: nothing is uploaded, and there is no account.