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meas·ure·ment

(mĕzhər-mənt)

1. The act of measuring or the process of being measured.

2. A system of measuring: measurement in miles.

3. The dimension, quantity, or capacity determined by measuring: the measurements of a room.

CONVERSION BETWEEN METRIC AND U.S. CUSTOMARY UNITS

FROM U.S. CUSTOMARY TO METRIC

When You Know	Multiply By	To Find
inches	25.4	millimeters
	2.54	centimeters
feet	30.48	centimeters
yards	0.91	meters
miles	1.61	kilometers
teaspoons	4.93	milliliters
tablespoons	14.79	milliliters
fluid ounces	29.57	milliliters
cups	0.24	liters
pints (liquid)	0.47	liters (liquid)
quarts (liquid)	0.95	liters (liquid)
gallons	3.79	liters
cubic feet	0.028	cubic meters
cubic yards	0.76	cubic meters
ounces	28.35	grams
pounds	0.45	kilograms
short tons (2,000 lbs)	0.91	metric tons
square inches	6.45	square centimeters
square feet	0.09	square meters
square yards	0.84	square meters
square miles	2.59	square kilometers
acres	0.40	hectares

FROM METRIC TO U.S. CUSTOMARY

When You Know	Multiply By	To Find
millimeters	0.04	inches
centimeters	0.39	inches
meters	3.28	feet
	1.09	yards
kilometers	0.62	miles
milliliters	0.20	teaspoons
	0.07	tablespoons
	0.03	fluid ounces
liters (liquid)	1.06	quarts (liquid)
	0.26	gallons
	4.23	cups
	2.12	pints (liquid)
cubic meters	35.31	cubic feet
	1.35	cubic yards
grams	0.035	ounces
kilograms	2.20	pounds
metric tons (1,000 kg)	1.10	short tons
square centimeters	0.155	square inches
square meters	1.20	square yards
square kilometers	0.39	square miles
hectares	2.47	acres

TEMPERATURE CONVERSION BETWEEN CELSIUS AND FAHRENHEIT

°C = (°F - 32) ÷ 1.8

°F = (°C × 1.8) + 32

UNITS OF THE INTERNATIONAL SYSTEM

The International System (abbreviated SI, for Système International, the French name for the system) was adopted in 1960 by the 11th General Conference on Weights and Measures. An expanded and modified version of the metric system, the International System addresses the needs of modern science for additional and more accurate units of measurement. The key features of the International System are decimalization, a system of prefixes, and a standard defined in terms of an invariable physical measure.

BASE UNITS

The International System has base units from which all others in the system are derived. The standards for the base units, except for the kilogram, are defined by unchanging and reproducible physical occurences. For example, the meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second. The standard for the kilogram is a platinum-iridium cylinder kept at the International Bureau of Weights and Standards in Sèvres, France.

Unit	Quantity	Symbol
meter	length	m
kilogram	mass	kg
second	time	s
ampere	electric current	A
kelvin	temperature	K
mole	amount of matter	mol
candela	luminous intensity	cd

PREFIXES

A multiple of a unit in the International System is formed by adding a prefix to the name of that unit. The prefixes change the magnitude of the unit by orders of ten from 1024 to 10-24.

Prefix	Symbol	Multiplying Factor
yotta-	Y	1024 = 1,000,000,000,000,000,000,000,000
zetta-	Z	1021 = 1,000,000,000,000,000,000,000
exa-	E	1018 = 1,000,000,000,000,000,000
peta-	P	1015 = 1,000,000,000,000,000
tera-	T	1012 = 1,000,000,000,000
giga-	G	109 = 1,000,000,000
mega-	M	106 = 1,000,000
kilo-	k	103 = 1,000
hecto-	h	102 = 100
deca-	da	10 = 10
deci-	d	10-1 = 0.1
centi-	c	10-2 = 0.01
milli-	m	10-3 = 0.001
micro-	μ	10-6 = 0.000,001
nano-	n	10-9 = 0.000,000,001
pico-	p	10-12 = 0.000,000,000,001
femto-	f	10-15 = 0.000,000,000,000,001
atto-	a	10-18 = 0.000,000,000,000,000,001
zepto-	z	10-21 = 0.000,000,000,000,000,000,001
yocto-	y	10-24 = 0.000,000,000,000,000,000,000,001

DERIVED UNITS

Most of the units in the International System are derived units, that is units defined in terms of base units and supplementary units. Derived units can be divided into two groups—those that have a special name and symbol, and those that do not.

WITHOUT NAMES AND SYMBOLS
Measure of	Derivation
acceleration	m/s2
angular acceleration	rad/s2
angular velocity	rad/s
density	kg/m3
electric field strength	V/m
luminance	cd/m2
magnetic field strength	A/m
velocity	m/s

WITH NAMES AND SYMBOLS
Unit	Measure of	Symbol	Derivation
coulomb	electric charge	C	A·s
farad	electric capacitance	F	A·s/V
henry	inductance	H	V·s/A
hertz	frequency	Hz	cycles/s
joule	quantity of energy	J	N·m
lumen	flux of light	lm	cd·sr
lux	illumination	lx	lm/m2
newton	force	N	kg·m/s2
ohm	electric resistance	Ω	V/A
pascal	pressure	Pa	N/m2
tesla	magnetic flux density	T	Wb/m2
volt	voltage	V	W/A
watt	power	W	J/s
weber	magnetic flux	Wb	V·s

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.