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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

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

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

Measurement

Symbol

Meter

Gram

Newton

Pascal

Kilonewton per cubic meter

Second

Distance

Mass

Force

Stress or pressure

Unit weight

Time

M

g

N

Pa

kN/m3

s

These units are often accompanied by the following prefixes.

TABLE 3 Common SI Prefixes

Prefix

Symbol

milli

centi

kilo

mega

m

c

k

M

Multiplier

10 -3

10 -2

103

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.

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CONVERSION FACTORS

The conversion factors in Tables 4¨C8 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/s 2 132.17 ft/s 22, 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

Multiply by

ft

ft

in.

in.

m

mm

in.

m

t

mm

ft

in.

12

0.3048

1/12

25.40

3.281

0.03937

TABLE 5 Units of Force

To Convert

To

Multiply by

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

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

3

ft

gal

To

Multiply by

gal

ft3

7.481

0.1337

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TABLE 7 Units of Stress and Pressure

To Convert

To

Multiply by

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

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

Multiply by

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

6.366

0.1020

0.1020

0.1571

9.807

9.807

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