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Unit Conversion Factors

ENGLISH UNITS The following English units are commonly used in geotechnical engineering.

TABLE 1 Common English Units

Unit Measurement Symbol

Foot Distance ft Inch Distance in. Pound Force or mass lb Kip (kilopound) Force kip Ton Force or mass t Second Time s Pound per square foot Stress or pressure lb/ft2 or psf Pound per square inch Stress or pressure lb/in.2 or psi Pound per cubic foot Unit weight lb/ft3 or pcf

SI AND METRIC UNITS The following SI (Système International) units are commonly used in geotechnical engineering.

TABLE 2 Common SI Units

Unit Measurement Symbol

Meter Distance M Gram Mass g Newton Force N Pascal Stress or pressure Pa Kilonewton per cubic meter Unit weight kN/m3 Second Time s

These units are often accompanied by the following prefixes.

TABLE 3 Common SI Prefixes

Prefix Symbol Multiplier

milli m 10-3 centi c 10-2 kilo k 103 mega M 106

Some non-SI metric units also are used, especially in Europe.The most common example is the use of kg/cm2 as a unit of stress. CVR_CODU8681_05_SE_BEP.QXD 3/1/10 5:16 PM Page 3

CONVERSION FACTORS The conversion factors in Tables 4–8 are useful for converting measurements between English, metric, and SI units. Most of these factors are rounded to four significant figures. Those in bold type are absolute conversion factors (e.g.,12 in. = 1 ft ). When units of force are equated to units of mass, the acceleration F = ma is presumed to be 1 2 9.807 m/s2 32.17 ft/s2 , which is the acceleration due to gravity on the earth’s surface. 1 2 There are at least three definitions for the word “ton”: the 2000-lb short ton (commonly used in the United States and Canada), the 2240-lb long ton (used in Great Britain), and the 2205-lb (1000 kg) metric ton (also known as a tonne). A useful approximate conversion factor: 1 short ton/ft2 L 1kg/cm2 L 100 kPa L 1 atmosphere. These are true to within 2 to 4%.

TABLE 4 Units of Distance

To Convert To Multiply by

ft in. 12 ft m 0.3048 in. t 1/12 in. mm 25.40 m ft 3.281 mm in. 0.03937

TABLE 5 Units of Force

To Convert To Multiply by

k kN 4.448 k lb 1000 kgf lb 2.205 kgf N 9.807 kgf ton (metric) 0.001 kN k 0.2248 lb k 0.001

lb kgf 0.4536 lb N 4.448 lb ton (short) 1/2000 lb ton (long) 1/2240 N kgf 0.1020 N lb 0.2248 ton (short) lb 2000 ton (long) lb 2240 ton (metric) kgf 1000

TABLE 6 Units of Volume

To Convert To Multiply by

ft3 gal 7.481 gal ft3 0.1337 CVR_CODU8681_05_SE_BEP.QXD 3/1/10 5:16 PM Page 4

TABLE 7 Units of Stress and Pressure

To Convert To Multiply by

atmosphere lb/ft2 2117 atmosphere kPa 101.3 bar kPa 100 2 kgf/cm kPa 98.07 2 2 kgf/cm lb/ft 2048 kPa atmosphere 0.009869 kPa bar 0.01 2 kPa kgf/cm 0.01020 kPa lb/ft2 20.89 kPa lb/in.2 0.1450 kPa metric ton/m2 0.1020 lb/ft2 atmosphere 4.725 * 10-4 lb/ft2 kPa 0.04787 lb/ft2 lb/in.2 1/144 lb/in.2 kPa 6.895 lb/in.2 lb/ft2 144 lb/in.2 MPa 6.895 * 10-3 metric ton/m2 kPa 9.807 MPa lb/in.2 145.0

TABLE 8 Units of Unit Weight

To Convert To Multiply by

kN/m3 lb/ft3 6.366 kN/m3 metric ton/m3 0.1020 3 3 kN/m Mgf/m 0.1020 lb/ft3 kN/m3 0.1571 metric ton/m3 kN/m3 9.807 3 3 Mgf/m kN/m 9.807