 hacienda

a large traditional unit of land area in Mexico and the southwestern U.S.
5 square leguas or 125 million square varas. Based on Texas definition of the
vara, would be about 8960 hectares or 22 140 acres (34.59 square miles). Using
the shorter Mexican vara, it would be about 8778 hectares or 21 690 acres.
 halbe

a German word for one half; often used as a unit of volume for beer and other
liquids equal to 1/2 maß (1/2 liter).
 half

a unit of proportion equal to 1/2.
 half step

a unit used in music to describe the ratio in frequency between notes. Equal to
1/12 octave, the half step measures the difference between adjacent notes in
the standard 12tone scale, as on a piano keyboard.
 hand

a traditional unit of distance. One hand equals 4 inches, 1/3 foot, or 10.16
centimeters.
 hank

a traditional measure of length for yarn. The length of yarn in a hank varies
with the market and the material. In the U.S., a hank of woolen yarn is
generally 1600 yards (1463 meters). In retail trade, a hank is often equal to 6
or 7 skeins of varying size.
 hardness

a measure of the hardness of a metal or mineral. Hardness is a property easy to
appreciate but difficult to quantify and measure.
 head

a unit of quantity for livestock, equal to one animal. No 's' is added for the
plural: e.g. "36 head" of cattle.
 heaped bushel

a traditional unit of volume in the United States, the heaped bushel is just
what its name implies: the volume of a bushel container filled to overflowing.
Officially, the heaped bushel was supposed to equal 1.278 regular, or "struck"
bushels, frequently interpreted as 1.25 bushels, which is equal to exactly 5
pecks, 2688.025 cubic inches, 1.5556 cubic feet, or 44.049 liters.
 heat index

a measure of the combined effect of heat and humidity on the human body.
 heating degree day (HDD)

see degree day.
 heat unit

an alternate name, coined by Americans, for the British thermal unit (Btu).
This is not the same as the Celsius heat unit (Chu).
 hect or hecto (h)

a metric prefix denoting 100, coined from the Greek word hekaton for one
hundred.
 hectare (ha)

the customary metric unit of land area, equal to 100 ares. One hectare is a
square hectometer, that is, the area of a square 100 meters on each side:
exactly 10 000 square meters or approximately 107 639.1 square feet, 11 959.9
square yards, or 2.471 054 acres.
 hectare meter(ha·m)

a unit of volume used to measure the capacity of reservoirs, equal to the
volume of water one meter deep covering one hectare. One hectare meter equals
exactly 10 000 cubic meters or about 8.1071 acre feet.
 hectobar (hbar)

a very common metric unit of pressure equal to 100 bars, 10 megapascals
(MPa), or 1 dekanewton per square millimeter
(daN/mm^{2}). This is approximately 1450.38 pounds per square inch
(lbf/in^{2} or psi) or 208 855 pounds (104.43 U.S. tons) per square
foot.
 hectogram (hg)

a common metric unit of mass, equal to 100 grams or about 3.5274 ounces.
 hectoliter (hL or hl)

a common metric unit of volume. The hectoliter equals 100 liters, 0.1 cubic
meter, 26.417 U.S. liquid gallons, 21.999 British imperial gallons, or 3.5315
cubic feet.
 hectometer (hm)

a metric unit of distance equal to 100 meters, 328.084 feet, or 109.361 yards.
 hectopascal (hPa)

a metric unit of pressure equal to 100 pascals or 0.1 kilopascal (kPa). The
hectopascal, used almost entirely in measurements of air pressure, is identical
to the millibar (mb). The SI unit for air pressure is the kilopascal.
 heer

a traditional measure of length for linen and woolen yarn, equal to 2 cuts or
1/6 hank (see above). This is equivalent to 80 yards (73.152 meters).
 helek (hl)

a traditional Hebrew unit of time equal to 1/1080 hour, 1/18 minute or 10/3
seconds. The plural is halakim. Halakim are used in formulas
establishing the instant of new moon, which marks the start of the month in the
Jewish calendar.
 hemina

a Roman unit of liquid volume, equal to 1/2 sextarius or about 265.6
milliliters (0.561 U.S. pint or 0.467 British Imperial pint).
 hemisphere

a traditional unit of solid angle equal to 1/2 sphere, 2pi
steradians, or about 20 626.48 square degrees.
 heptad

a unit of quantity equal to 7.
 hertz (Hz)

the SI unit of frequency, equal to one cycle per second. The hertz is used to
measure the rates of events that happen periodically in a fixed and definite
cycle. Multiples of the hertz are common: the frequencies of radio and
television waves are measured in kilohertz (kHz), megahertz (MHz), or even
gigahertz (GHz), and the frequencies of light waves in terahertz (THz). The
unit is named for the German physicist Heinrich Rudolf Hertz (18571894), who
proved in 1887 that energy is transmitted through a vacuum by electromagnetic
waves.
 hexad

a unit of quantity equal to 6.
 hexit

a unit of information equal to 4 bits or 1/2 byte. A string of 4 bits has 16
possible states (015) and is usually represented as a single base16, or hexadecimal,
digit (in the hexadecimal system the letters A through F are used to
represent the numbers 10 through 15, respectively). A hexit of data is also
known as a nibble or a quadbit.
 hin

an ancient Hebrew unit of liquid capacity, mentioned in the Bible. The unit
varied in size over time, but typically it was around 3.7 liters, a little
smaller than the U.S. gallon.
 hold

one of two Hungarian units of land area. The traditional magyar hold
or Hungarian acre is equal to 1200 square öl (fathoms) or about 0.4314 hectare
(1.066 acres).
 homestead

a historic unit of area in the United States, equal to 160 acres (64.75
hectares). A homestead equals 1/4 square mile, or 1/4 section in U.S.
government terminology.
 horse

slang for the horsepower.
 horsepower (hp)

a unit of power representing the power exerted by a horse in pulling. The
horsepower was defined by James Watt (17361819), the inventor of the steam
engine, who determined after careful measurements that a horse is typically
capable of a power rate of 550 footpounds per second. The SI unit of power is
named for Watt, and one horsepower is equal to approximately 745.6999 watts.
 horsepower hour (hp hr)

a unit of work or energy equal to the work done at the rate of 1 horsepower for
1 hour. The horsepower hour equals 1 980 000 foot pounds or approximately 2.685
megajoules, 2545 Btu, 641.1 (large) Calories, or 745.7 watt hours.
 hour (h or hr)

a traditional unit of time, equal to 60 minutes, or 3600 seconds, or 1/24 day.
Originally an hour was 1/12 of the time between sunrise and sunset, so summer
hours were longer than winter hours. Later, when people wanted to express times
at night, it was natural to divide the night into 12 hours as well, making 24
hours in the day. The word comes from an ancient Greek word hora which
originally meant a season, especially a religious season, and hence a "defined"
period of time.

a unit of angular measure used in astronomy, equal to 1/24 circle or 15°.
Latitude is measured in degrees from the equator to the poles, just as it is on
the surface of the earth. Longitude is replaced by right ascension, measured in
hours from the longitude, traditionally known as the First Point of Aries, at
which the Sun crosses the equator on its northward journey in the spring.
 hu

a traditional Chinese unit of liquid volume. The hu contains about 51.77
liters, 13.676 U.S. gallons, or 11.389 British imperial gallons.
 hue

a numerical measure of color; see color units.
 hundredweight (Cwt or cwt)

a traditional unit of weight equal to 1/20 ton.
