How this instrument works
Deci- and centi- were born together. The French law of 18 germinal, year III — spring 1795 — assigned Latin names to the metre's submultiples: déci for one tenth, centi for one hundredth, milli for one thousandth. That single stroke fixed the ratio between a decimetre and a centimetre at exactly ten, forever, regardless of how the metre itself was later redefined against krypton light or the speed of light in a vacuum.
Both units move together whenever the metre's definition changes, so their ten-to-one relationship has never once needed correction. Ten is notation, not observation: no laboratory measured it, no committee revised it, and no digit past the decimal point in this conversion is ever uncertain. Only your own entry decides how many decimals appear in the answer.
Centimetres won the everyday contest that decimetres lost. Tape measures, height charts, dress patterns and rulers are marked in centimetres and millimetres almost everywhere metric units are used, while a bare decimetre scale is rare enough that most people never see one on a physical tool. Decimetres survive mainly in specialist corners — Scandinavian conversational speech, some European schoolbooks teaching the metric ladder, and the definition of the litre as one cubic decimetre — which is exactly why a stray '10 dm' on a supplier's spec sheet needs converting rather than reading at a glance.
- Type your figure into the Decimetres (dm) field; it opens at 10 as a reference point.
- Read your answer on the Centimetres (cm) line, recalculated to six decimal places on every keystroke.
- Check it mentally — decimetres to centimetres is always the same digits with the decimal point shifted one place right.
- Need centimetres back to decimetres? Divide by 10 instead, moving that point one place left.
Worked example — a 10 dm spool of grosgrain ribbon
Notions counters in parts of continental Europe still price trim and ribbon by the decimetre out of old habit, so a haberdasher's ticket might read '10 dm' for a spool. Type 10 into Decimetres (dm) and Centimetres (cm) reads 100 — the figure a dressmaker's tape actually shows, since almost no household tape is graduated in decimetres at all.
The arithmetic never gets messier than this: 10 × 10 = 100 on paper exactly as it does here, and writing that same length as 1000 mm or 1.0 m agrees digit for digit. The one genuine hazard is the symbol itself — mistake dm for dam (decametre) and 10 dam becomes 1000 cm, a hundredfold jump that would turn one modest ribbon order into enough trim to wrap a house.
Questions
Is the factor of 10 here exact, or has it been rounded?
Exact, and settled by definition rather than by measurement. SI prefixes are fixed powers of ten — deci- is 10⁻¹ of a base unit, centi- is 10⁻² — so a decimetre is always exactly ten centimetres, with zero uncertainty. This has held since France's 1795 nomenclature law and survives every later redefinition of the metre itself, because decimetres and centimetres are both tied to that same metre and move in lockstep.
What is the difference between dm and dam?
A factor of one hundred, and confusing the two is the single most common slip on this page. Lowercase dm means decimetre, one tenth of a metre; dam means decametre, ten metres. A decametre is ten thousand times larger than a decimetre, so if a converted answer looks two orders of magnitude off, check that symbol before anything else — obsolete forms like Dm or dkm for decametre only add to the confusion.
Why don't rulers show decimetre markings?
Because centimetres and millimetres already cover that range in finer, more useful steps. A 30 cm ruler could in principle carry three decimetre marks, but manufacturers rarely bother, since anyone reading a ruler wants centimetre or millimetre precision anyway. Decimetres survive as a unit of calculation and conversation rather than a unit you measure directly against a physical scale.
Is a cubic decimetre really the same as a litre?
Yes, exactly, since the 12th General Conference on Weights and Measures redefined the litre in 1964 as precisely one cubic decimetre. Before that date, from 1901, a litre was defined instead as the volume of one kilogram of pure water at its densest — a figure that turned out to be 1.000028 cubic decimetres, a tiny but real gap that mattered to precision volumetric chemistry of that era. Today the two are identical by decision, not by measurement.
Who still uses decimetres in everyday speech?
Mostly Nordic speakers. Swedish and Norwegian routinely use decimeter in conversation where an English speaker would say centimetres or a fraction of a metre — describing a shelf, a plank, or a person's stride, for instance. Elsewhere the unit survives mainly in classrooms teaching the metric ladder from millimetre up to kilometre, and in specialist fields like UHF radio, where wavelengths between 1 dm and 10 dm are called decimetric waves.
How many inches is a decimetre?
About 3.937008 inches, or exactly 500⁄127. That fraction traces back to 1959, when six countries fixed the international inch at precisely 25.4 mm, so this too is a matter of definition rather than measurement. It never terminates as a decimal — 3.9370078740157… continues indefinitely — which is why any inch conversion from a metric figure like decimetres is shown to a fixed number of decimal places rather than in full.