Convert kilometers to decimeters

Both units take their value from the meter, the base unit of length in the SI, and both get it from a prefix written in front. The prefix kilo- stands for a thousand and the prefix deci- for one tenth[1]. A kilometer is therefore a thousand meters, and a decimeter is one tenth of a meter.

Four steps of ten separate the two units, and that is where the multiplier of ten thousand comes from. Going down from the kilometer, the next steps are the hectometer at a hundred meters, the decameter at ten meters and the meter itself. The decimeter is one step below the meter. Both middle steps have their own symbols in the table of SI prefixes: hm for the hectometer and dam for the decameter[1].

The kilometer measures distances on land. The English article calls it "the preferred measurement unit to express distances between geographical places on land in most of the world" and names the United States, the United Kingdom and Liberia as the places where the statute mile serves that purpose[2].

The decimeter describes lengths measured at close range, and the English article lists three settings where it is the working unit: the liter is defined as one cubic decimeter, the path length in a polarimeter is given in decimeters, and ship's draft markings are shown in decimeters in most of the world[3].

Which unit you use depends on the size of the thing you are measuring. Kilometers describe routes and distances between places, decimeters describe object sizes and lengths read off a rule. The conversion helps when one value has to be used in a calculation done in the other unit: a homework question, a spreadsheet column of dimensions, or an instrument reading labeled differently from the rest of a document.

A kilometer is 10,000 decimeters. Two kilometers give 20,000 decimeters, and five kilometers give 50,000 decimeters.

Every conversion in this direction comes down to multiplying the number of kilometers by ten thousand. Half a kilometer is 5,000 decimeters. A quarter of a kilometer gives 2,500 decimeters. One hundred meters, which is one tenth of a kilometer, is 1,000 decimeters.

For whole kilometers the result ends in four zeros added to their number, so those values come straight from memory. Eight kilometers is 80,000 decimeters. Thirteen kilometers gives 130,000 decimeters.

For values with a decimal point, the point itself moves four places to the right. 8.24 km becomes 82,400 dm. 0.005 km becomes 50 dm.

The converter above works in both directions and shows the result while you type. For numbers from a thousand up it repeats the result under the field on a line labeled Scientific notation, so you do not have to work out the power of ten yourself.

The conversion rests on a fixed relation: one kilometer is 10,000 decimeters. To turn kilometers into decimeters you multiply their number by ten thousand.

The full formula: decimeters = kilometers × 10,000. The other way round: kilometers = decimeters ÷ 10,000.

Three examples of different size come out of that formula. A value of 0.54 km multiplied by ten thousand gives 5,400 decimeters. A stretch of 22.5 km gives 225,000 decimeters. A route of 515 km gives 5,150,000 decimeters, and the same number in scientific notation reads 5.15 × 10⁶ dm.

In writing, the multiplication changes only the position of the decimal point. The digits stay as they are and the point moves four places to the right. 1.5 kilometers becomes 15,000 decimeters, and 0.2 kilometers becomes 2,000 decimeters. You fill the empty places with zeros.

The other way round the operation is reversed: you divide by ten thousand and the point moves four places to the left. That is what the decimeters to kilometers converter does. If your value is written in meters, use the meters to kilometers converter, and for the step below the decimeter use the decimeters to centimeters converter.