Unit Conversion Factors

[Pages:3]Unit Conversion Factors

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

TABLE 1 Common English Units

Unit

Measurement

Foot Inch Pound Kip (kilopound) Ton Second Pound per square foot Pound per square inch Pound per cubic foot

Distance Distance Force or mass Force Force or mass Time Stress or pressure Stress or pressure Unit weight

Symbol

ft in. lb kip t s lb/ft2 or psf lb/in.2 or psi lb/ft3 or pcf

SI AND METRIC UNITS

The following SI (Syst?me International) units are commonly used in geotechnical engineering.

TABLE 2 Common SI Units

Unit

Meter Gram Newton Pascal Kilonewton per cubic meter Second

Measurement

Distance Mass Force Stress or pressure Unit weight Time

Symbol

M g N Pa kN/m3 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.

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 1F = ma2 is presumed to be 9.807 m/s2 132.17 ft/s22, which is the acceleration due to gravity on the earth's surface.

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

ft

in.

ft

m

in.

t

in.

mm

m

ft

mm

in.

Multiply by

12 0.3048 1/12 25.40 3.281 0.03937

TABLE 5 Units of Force

To Convert

To

k k kgf kgf kgf kN lb

lb

lb lb lb N N ton (short) ton (long) ton (metric)

kN lb lb N ton (metric) k k

kgf N ton (short) ton (long) kgf lb lb lb kgf

Multiply by

4.448 1000 2.205 9.807 0.001 0.2248 0.001

0.4536 4.448 1/2000 1/2240 0.1020 0.2248 2000 2240 1000

TABLE 6 Units of Volume

To Convert

To

ft3

gal

gal

ft3

Multiply by

7.481 0.1337

TABLE 7 Units of Stress and Pressure

To Convert

To

atmosphere

atmosphere

bar kgf/cm2 kgf/cm2

kPa

kPa

kPa

kPa

kPa

kPa lb/ft2 lb/ft2 lb/ft2 lb/in.2 lb/in.2 lb/in.2 metric ton/m2

MPa

lb/ft2

kPa

kPa

kPa lb/ft2

atmosphere

bar kgf/cm2

lb/ft2 lb/in.2 metric ton/m2

atmosphere

kPa lb/in.2

kPa lb/ft2

MPa

kPa lb/in.2

Multiply by

2117 101.3 100 98.07 2048 0.009869 0.01 0.01020 20.89 0.1450 0.1020 4.725 * 10-4 0.04787 1/144 6.895 144 6.895 * 10-3 9.807 145.0

TABLE 8 Units of Unit Weight

To Convert

To

kN/m3 kN/m3 kN/m3 lb/ft3 metric ton/m3 Mgf/m3

lb/ft3 metric ton/m3

Mgf/m3 kN/m3 kN/m3 kN/m3

Multiply by

6.366 0.1020 0.1020 0.1571 9.807 9.807

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