Useful Measurement Equivalents
Length
1 inch = 2.54 centimeters
1 foot = 12 inches = 30.49 centimeters
1 yard = 3 feet = 36 inches = 91.44 centimeter (0.914 4 meter)
1 (statute mile) = 5280 feet = 1.609 kilometers
Area
1 square foot = 144 sq inches =6.45 square centimeters
1 square yard = 9 square feet =0.836 square meters
1 acre = 43 560 square feet = 0.404 Hectare (4046 sq. meters)
1 square mile = 640 acres =258.9 Hectares or 2.5 million square meters
Volume
1 cubic foot= 1728 cubic inches = 28.31 liters
1 cubic yard= 27 cubic feet =0.7645 cubic meters
1 quart (liquid) = 2 pints = 32 fluid ounces =946 milliliters (0.946 liter)
1 peck = 8 quarts = 8.8 liters
1 bushel = 4 pecks = 32 quarts = 35.23 liters
1 dry pint = 550 milliliters
1 dry quart = 1.1 liter
Weight (mass)
1 oz = 28.35 grams
1 pound = 16 ounces = 453.59 grams (0.453 59 kilogram)
1 ton = 2000 pounds = 907 kilograms (0.907 metric ton)
1 long ton = 2240 pounds = 1016 kilograms (1.102 metric tons)
ALL EQUIVALENTS
When the name of a unit is enclosed in brackets (thus, [1 hand] . . . ), this indicates (1) that the unit is not in general current use in the United States, or (2) that the unit is believed to be based on "custom and usage" rather than on formal authoritative definition.
Equivalents involving decimals are, in most instances, rounded off to the third decimal place except where they areexact, in which cases these exact equivalents are so designated. The equivalents of the imprecise units "tablespoon"and "teaspoon" are rounded to the nearest milliliter.
UNITS OF LENGTH
0.1 nanometer (exactly).
0.000 1 micrometer (exactly).
angstrom (D)10----------------------- 0.000 000 1 millimeter (exactly).
1 cable’s length----------------------- 720 feet (exactly).
1 centimeter (cm)---------------------- 0.393 7 inch.
1 chain (ch)--------------------------- 66 feet (exactly)
1 decimeter (dm)----------------------- 3.937 inches.
1 fathom------------------------------- 1.828 8 meters.
1 foot (ft)---------------------------- 0.304 8 meter (exactly).
1 furlong (fur)------------------------ 660 feet (exactly).
[1 hand]------------------------------- 4 inches.
1 inch (in)---------------------------- 2.54 centimeters (exactly).
1 kilometer (km)----------------------- 0.621 mile.
1 league (land)------------------------ 3 U.S. statute miles (exactly).
1 link (li) (Gunter’s or surveyors)---- 0.201 168 meter.
1 meter (m)---------------------------- 39.37 inches.
1 micrometer--------------------------- 0.001 millimeter (exactly).
1 mil---------------------------------- 0.025 4 millimeter (exactly).
1 mile (mi) (U.S. statute)11 ---------- 5280 feet survey (exactly).
1 mile (mi) (international)------------ 5280 feet international (exactly).
1 mile (mi) (international nautical)------------- 1.852 kilometers (exactly).
1 millimeter (mm)---------------------- 0.039 37 inch.
0.001 micrometer (exactly).
1 nanometer (nm)----------------------- 0.000 000 039 37 inch.
1 Point (typography)------------------- 1/72 inch (approximately).
1 rod (rd), pole, or perch------------- 16 1/2 feet (exactly).
1 yard (yd)---------------------------- 0.914 4 meter (exactly).
UNITS OF AREA
43 560 square feet (exactly).
1 acre13---------------------------- 0.405 hectare.
1 are------------------------------ 119.599 square yards.
0.025 acre.
1 hectare-------------------------- 2.471 acres.
[1 square (building)]--------------- 100 square feet.
1 square centimeter (cm2)----------- 0.155 square inch.
1 square decimeter (dm2)------------ 15.500 square inches.
1 square foot (ft2)----------------- 929.030 square centimeters.
1 square inch (in2)----------------- 6.451 6 square centimeters (exactly).
1 square kilometer (km2)------------ 247.104 acres.
1 square meter (m2)----------------- 1.196 square yards.
1 square mile (mi2)----------------- 258.999 hectares.
1 square millimeter (mm2)----------- 0.002 square inch.
1 square rod (rd2), sq pole,
or sq perch----------------------- 25.293 square meters.
1 square yard (yd2)----------------- 0.836 square meter.
UNITS OF CAPACITY OR VOLUME
1 barrel (bbl), liquid----------------- 31 to 42 gallons.14
1 barrel (bbl), standard for fruits, 7056 cubic inches.
vegetables, and other dry------------ 105 dry quarts.
1 barrel (bbl), standard, cranberry---- 86 45/64 dry quarts.
1 bushel (bu) (U.S.) struck measure---- 35.239 liters.
[1 bushel, heaped (U.S.)]-------------- 1.278 bushels
1 cord (cd) (firewood)----------------- 128 cubic feet (exactly).
1 cubic centimeter (cm3)--------------- 0.061 cubic inch.
1 cubic decimeter (dm3)---------------- 61.024 cubic inches.
1 cubic foot (ft3)--------------------- 7.481 gallons.
1 cubic inch (in3)------------------------ 4.433 fluid drams.
1 cubic meter (m3)--------------------- 1.308 cubic yards.
1 cubic yard (yd3)--------------------- 0.765 cubic meter.
1 cup, measuring----------------------- 237 milliliters.
1 dekaliter (daL)---------------------- 2.642 gallons.
1 dram, fluid (or liquid) (fl dr 0.226 cubic inch.
or ƒ ) (U.S.)------------------------ 3.697 milliliters.
[1 drachm, fluid (fl dr) (British)]---- 0.217 cubic inch.
1 gallon (gal) (U.S.)------------------ 0.833 British gallon.
[1 gallon (gal) (British Imperial)]---- 4.546 liters.
1 gill (gi)---------------------------- 4 fluid ounces (exactly).
1 hectoliter (hL)---------------------- 26.418 gallons.
1 liter (1 cubic decimeter exactly)---- 0.908 dry quart.
1 milliliter (mL)---------------------- 16.231 minims.
[1 ounce, fluid (fl oz) (British)]----- 1.734 cubic inches.
1 peck (pk)---------------------------- 8.810 liters.
1 pint (pt), dry----------------------- 0.551 liter.
28.875 cubic inches exactly.
1 pint (pt), liquid-------------------- 0.473 liter.
1 quart (qt), dry (U.S.)--------------- 1.101 liters.
1 quart (qt), liquid (U.S.)------------ 0.946 liter.
[1 quart (qt) (British)]--------------- 1.032 U.S. dry quarts.
1 tablespoon, measuring---------------- 15 milliliters.
1 teaspoon, measuring------------------ 5 milliliters.
1 water ton (English)------------------ 224 British Imperial gallons.
UNITS OF MASS
1 assay ton (AT)--------------------- 29.167 grams.
1 carat (c)---------------------------- 3.086 grains.
1 dram apothecaries (dr ap or )----- 60 grains (exactly).
1 dram avoirdupois (dr avdp)----------- 27-11/32 (= 27.344) grains.
1 gamma ( )--------------------------- 1 microgram (exactly).
1 grain-------------------------------- 64.798 91 milligrams (exactly).
1 gram (g)----------------------------- 15.432 grains.
1 hundredweight, gross or long18 112 pounds (exactly).
(gross cwt)-------------------------- 50.802 kilograms.
1 hundredweight, gross or short 100 pounds (exactly).
(cwt or net cwt)--------------------- 45.359 kilograms.
1 kilogram (kg)------------------------ 2.205 pounds.
1 microgram (µg) [the Greek letter mu
in combination with the letter g]--- 0.000 001 gram (exactly).
1 milligram (mg)----------------------- 0.015 grain.
1 ounce, avoirdupois (oz avdp)--------- 0.911 troy or apothecaries ounce.
(oz t or oz ap or )---------------- 1.097 avoirdupois ounces.
1 pennyweight (dwt)-------------------- 1.555 grams.
1 point-------------------------------- 0.01 carat.
1 pound, avoirdupois (lb avdp)--------- 1.215 troy or apothecaries pounds.
1 pound, troy or apothecaries 5760 grains (exactly).
(lb t or lb ap)---------------------- 0.823 avoirdupois pound.
1 scruple (s ap or )---------------- 20 grains (exactly).
1 ton, gross or long----------------- 1.12 net tons (exactly).
1 ton, metric (t)---------------------- 0.984 gross ton.
1 ton, net or short-------------------- 0.893 gross ton.
A Capsule History - Definition of the Meter
The United States is now the only industrialized country in the world that does not use the metric system as its predominant system of measurement.
Most Americans think that our involvement with metric measurement is relatively new. In fact, the United States has been increasing its use of metric units for many years, and the pace has accelerated in the past three decades.
The metric system is simple to learn and easy to use. For use in your every-day life you will need to learn about ten new units. You will also need to get used to a few new temperatures. There are some metric units with which you are already familiar: those for time and electricity are the same as you use now. The basic units of the metric system are the meter, which is a unit of length; the gram, which is a unit of weight; and the liter, which is a unit of capacity or volume. Other units in the metric system are the decimal subdivisions and multiples of the basic units, named by combining the proper prefix with the name of the basic unit to form self-defining terms.
The current effort toward national metrication is based on the conclusion that industrial and commercial productivity, mathematics and science education, and the competitiveness of American products and services in world markets, will be enhanced by completing the change to the metric system of units. Failure to complete the change will increasingly handicap the Nation's industry and economy.
Time Line
1791 |
The International System (formerly called the Metric System) is the decimal system of weights and measures based on the meter and the kilogram. The essential features of the system were embodied in a report to the French National Assembly by the Paris Academy of Sciences. |
1799 |
Originally intended to be one ten-millionth part of the quadrant of the earth, the so called Meter of the Archives was based on a measurement of a meridian between Dunkirk and Barcelona. A platinum bar with a rectangular cross section and polished parallel ends was made to embody the meter. The meter was defined as the distance between the polished end faces at a specified temperature and it was the international standard for most of the 19th century. It was compared to other bars with optical comparators as a means of disseminating the unit. |
1859 |
J.C. Maxwell suggested choosing as a natural standard, the wavelength of the yellow spectral line of sodium. |
1866 |
By act of the U.S. Congress, the use of the metric system was legalized in this country, but was not made obligatory. |
1872 |
The International Commission of the Meter made the Meter of the Archives the official definition of the meter and the standard of length. It was admitted that its relationship to a quadrant of the earth was tenuous and of little consequence anyway. The Commission had 30 prototype meters made using the Meter of the Archives as the reference. |
1875 |
On May 20, the Treaty of the Meter was signed by twenty countries, including the United States, at the International Metric Convention. . |
1889 |
A new modified Xshaped cross-section graduated platinum-iridium line standard was developed and adopted as the International Prototype Meter. The meter was defined as the distance between the two graduation lines at 0 °C. Each member country in the International Metric Convention received two copies of the standard with calibration reports relating them to the prototype. All meter bar calibrations were done by comparisons in optical comparators. Prototype Meter No.27 served as the U.S. primary standard from 1889 to 1960. Its length is known in terms of the international prototype, having been returned to BIPM for recomparison four times during that period. It is now on exhibit in the NIST Museum at Gaithersburg, Maryland. |
1890 |
A.A. Michelson found that the red spectral line of natural cadmium was exceptionally coherent. |
1892 |
Michelson used an interferometer that he developed to determine the length of the International Prototype Meter in terms of the cadmium red line wavelength. His measurements gave the meter a value of 1,553,164.13 times the wavelength of cadmium red in air, at 760 mm of atmospheric pressure at 15 °C. |
1921 |
A. Perard began a systematic study of the radiations of cadmium, mercury, helium, neon, krypton, zinc and thallium, to determine which might best serve as defining lengths. |
1925 |
The Michelson interferometer was in regular use at BIPM for measuring length. |
1950 |
Cadmium 114, mercury 198, and krypton 86 were candidates to be a new definition of the meter based on the wavelength of light. |
1960 |
On October 14, the Eleventh General Conference on Weights and Measures redefined the International Standard of Length as 1,650,763.73 vacuum wavelengths of light resulting from unperturbed atomic energy level transition 2p10 5d5 of the krypton isotope having an atomic weight of 86. The wavelength is ? = 1 m / 1,650,763.73 = 0.605,780,211 µm At different times some national laboratories used light sources other than krypton 86 as length standards. Mercury 198 and cadmium 114 were among these and they were accepted by the General Conference as secondary length standards. |
1964 |
Helium-Neon stabilized laser wavelengths were coming into use as length standards. Although the laser wavelength was generally accepted as a secondary standard, its widening use was mainly based on its remarkable coherence. Long distances could be measured by laser interferometry that would be impossible with atomic light sources. Line scales of length are measured by dynamic (fringe counting) laser interferometry at NIST. |
1980 |
The iodine stabilized Helium-Neon laser wavelength was accepted as a length standard. It had a wavelength uncertainty of 1 part in 1010 at the time. |
1983 |
On October 20, the meter was redefined again. The definition states that the meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The speed of light is c = 299,792,458 m/s The second is determined to an uncertainty, U = 1 part in 1014 by the Cesium clock. The General Conference made the iodine stabilized Helium-Neon laser a recommended radiation for realizing the meter at this time. The wavelength of this laser is ?HeNe = 632.99139822 nm with an estimated relative standard uncertainty (U) of ± 2.5 x 10-11. In all of these changes in definition, the goal was not only to improve the precision of the definition, but also to change its actual length as little as possible. |
BRITISH UNITS OF MEASUREMENT
In Great Britain, the yard, the avoirdupois pound, the troy pound, and the apothecaries pound are identical with the unitsof the same names used in the United States. The tables of British linear measure, troy mass, and apothecaries massare the same as the corresponding United States tables, except for the British spelling "drachm" in the table of apothecaries mass. The table of British avoirdupois mass is the same as the United States table up to 1 pound;
14 pounds = 1 stone
2 stones = 1 quarter = 28 pounds
4 quarters = 1 hundredweight = 112 pounds
20 hundredweight = 1 ton = 2240 pounds
The present British gallon and bushel--known as the "Imperial gallon" and "Imperial bushel"--are, respectively, about 20 percent and 3 percent larger than the United States gallon and bushel. The Imperial gallon is defined as the volume of 10 avoirdupois pounds of water under specified conditions, and the Imperial bushel is defined as 8 Imperial gallons.
Also, the subdivision of the Imperial gallon as presented in the table of British apothecaries fluid measure differs in two important respects from the corresponding United States subdivision, in that the Imperial gallon is divided into 160 fluid ounces (whereas the United States gallon is divided into 128 fluid ounces), and a "fluid scruple" is included. The full table of British measures of capacity (which are used alike for liquid and for dry commodities) is as follows:
4 gills = 1 pint
2 pints = 1 quart
4 quarts = 1 gallon
2 gallons = 1 peck
8 gallons (4 pecks) = 1 bushel
8 bushels = 1 quarter
The full table of British apothecaries measure is as follows:
20 minims = 1 fluid scruple
3 fluid scruples = 1 fluid drachm= 60 minims
8 fluid drachms = 1 fluid ounce
20 fluid ounces = 1 pint
8 pints = 1 gallon (160 fluid ounces)