Conversion from 20 Decimeters to Hands

Information about the Decimeter (dm)

The decimetre is one tenth of a metre, written dm. It is a legitimate SI-derived unit formed with the prefix deci, but it is among the least used members of the metric ladder. Most people move directly from centimetres to metres and skip the intermediate step entirely.

The reason is practical rather than technical. A length of 3 dm is more naturally expressed as 30 cm or 0.3 m, and neither alternative requires the reader to pause. Units survive when they answer a question no neighbouring unit answers as well, and the decimetre rarely does.

One derived form is a striking exception. The cubic decimetre, dm³, is exactly one litre, because a cube measuring 10 cm on each side holds precisely that volume. This relationship is the foundation of the metric volume system and was deliberate: the litre was defined in 1795 as the volume of a cubic decimetre. The unit therefore appears constantly in chemistry, where concentration is expressed in moles per cubic decimetre, written mol/dm³. School and university chemistry courses use this notation routinely even though the same quantity could be written as moles per litre.

The square decimetre sees occasional use in specifying small areas, particularly in materials testing and in some European technical standards for coatings and surface treatment.

Outside these niches the decimetre appears mainly in teaching, where the full sequence of prefixes is demonstrated, and in tables of unit conversions. Some countries have used it historically for shoe sizing and for textile measurement.

Aquarium and tank capacities show the same relationship at work. A tank measuring five by three by four decimetres holds sixty cubic decimetres, which is sixty litres, and the arithmetic can be done without conversion factors. This is the practical advantage the metric system was designed to deliver, and the decimetre is the length at which volume in litres and length in whole units line up most neatly.

Scandinavia is the exception to its general neglect. Swedish, Norwegian and Danish speakers use the decimetre in ordinary conversation, giving the size of a fish, a shelf or a snowfall in decimetres where a French or German speaker would say tens of centimetres. Schools there teach it alongside the centimetre and the metre rather than skipping it, and rulers are marked accordingly. The habit is a reminder that which prefixes feel natural is a matter of custom rather than logic: the SI offers the whole ladder, and each language community has quietly settled on the rungs it finds comfortable.

One decimetre equals 10 centimetres, 100 millimetres, or 0.1 metres. It is approximately 3.937 inches, a little under four inches.

Information about the Hand (hh)

The hand is a unit of length equal to exactly four inches, or 101.6 millimetres. It survives in one specialised application: measuring the height of horses and ponies. Almost nowhere else is it still in use.

The measurement is taken from the ground to the withers, the ridge between the shoulder blades where the neck meets the back. The withers are chosen because they are a fixed skeletal point that does not move as the horse raises or lowers its head, so the figure is reproducible in a way that measuring to the top of the head would not be.

Notation is unusual and frequently misread. Heights are written with a decimal point that does not indicate a decimal fraction. A horse of 15.2 hands stands fifteen hands and two inches, which is 62 inches or 157.5 centimetres. Because a hand is four inches, the digit after the point runs only from 0 to 3, and 15.4 is not a valid height. The abbreviation hh, for hands high, is common.

The boundary between a pony and a horse is conventionally set at 14.2 hands, though the exact threshold varies between breed registries and competitive disciplines. Draught breeds such as the Shire commonly exceed 17 hands. The tallest horses on record have stood over 20 hands.

The unit derives from the breadth of a human palm, an origin shared with several ancient measures. Egyptian and Roman systems both used a palm of comparable size. Its standardisation at four inches in England is usually credited to a statute of Henry VIII. The persistence of the hand in equestrian use is largely conservatism, and metric heights in centimetres are now given alongside it in international competition rules.

Measuring accurately is harder than it appears. The horse must stand square on level ground with its head in a natural position, and a purpose-made measuring stick with a spirit level and sliding crossbar is used rather than a tape. Shoeing adds height, so official measurements specify whether the horse is shod, and competition rules that impose height limits require certification by an appointed measurer.

One hand equals 4 inches, 101.6 millimetres, or 0.1016 metres.