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.
| Unit | Symbol | 1 Hand equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Ångström | Å | 1016000000 Å | 9.84251968504 × 10-10 hh | Hands to Ångströms |
| Nanometer | nm | 101600000 nm | 0.00000000984251968504 hh | Hands to Nanometers |
| Micrometer | μm | 101600 μm | 0.00000984251968504 hh | Hands to Micrometers |
| Millimeter | mm | 101.6 mm | 0.00984251968504 hh | Hands to Millimeters |
| Centimeter | cm | 10.16 cm | 0.0984251968504 hh | Hands to Centimeters |
| Decimeter | dm | 1.016 dm | 0.984251968504 hh | Hands to Decimeters |
| Meter | m | 0.1016 m | 9.84251968504 hh | Hands to Meters |
| Decameter | dam | 0.01016 dam | 98.4251968504 hh | Hands to Decameters |
| Hectometer | hm | 0.001016 hm | 984.251968504 hh | Hands to Hectometers |
| Kilometer | km | 0.0001016 km | 9842.51968504 hh | Hands to Kilometers |
| Inch | in | 4 in | 0.25 hh | Hands to Inches |
| Foot | ft | 0.333333333333 ft | 3 hh | Hands to Feet |
| Yard | yd | 0.111111111111 yd | 9 hh | Hands to Yards |
| Chain | ch | 0.00505050505051 ch | 198 hh | Hands to Chains |
| Furlong | fur | 0.000505050505051 fur | 1980 hh | Hands to Furlongs |
| Mile | mi | 0.0000631313131313 mi | 15840 hh | Hands to Miles |
| Nautical mile | nmi | 0.0000548596112311 nmi | 18228.3464567 hh | Hands to Nautical miles |
| League | lea | 0.0000210437710438 lea | 47520 hh | Hands to Leagues |
| Nautical league | nlea | 0.000018286537077 nlea | 54685.0393701 hh | Hands to Nautical leagues |
| Astronomical unit | au | 6.79154051622 × 10-13 au | 1472419987205 hh | Hands to Astronomical units |
| Light year | ly | 1.07391284737 × 10-17 ly | 9.31174259112 × 1016 hh | Hands to Light years |
| Parsec | pc | 3.29263175808 × 10-18 pc | 3.03708423375 × 1017 hh | Hands to Parsecs |