T4. Unit Conversions

Elastic Constants - Strength - Density & Thermal Coefficients - Unit Conversions Tables


The S.I. and English Systems
The System International (International Standard System) of units uses units of Newtons (N) and meters (m) for its units of force and length. The English System (imperial, engineering) uses pounds (lb, force) and feet (ft) or inches (in). The unit of time, seconds (sec) is the same in both systems.

Below are various tables that convert units from English to S.I. and back (e.g., 1 meter = 39.4 inches), as well as common conversions within each system (e.g., 1 ft = 12 inches). In general, the Conversion Factors are listed to 6 significant digits (even though your answer should not be that extensive).

4a. Geometric Conversions
4b. Force and Stress Conversions

4c. Same System Conversions
4d. Pounds, Newtons & Kilograms;  Density
4e. Temperature

A useful interactive conversion tool, with many more units, is Engineering Exchange's online Unit Conversions program. Another tool, by Joshua Madison, may be downloaded here (no length conversions; remember, pressure has the same units as stress).

Some useful approximate conversions:
  • A pound is 4.45 newtons; a meter is 39.4 inches.
  • Multiply psi (or ksi) by ~7 to convert to kPa (or MPa)

4a. Lengths, Areas and Volumes - English Units to S.I. Units and Back

To Convert From
multiply
to get / To Convert from
multiply by
to get
Length
inches, in
25.4
millimeters, mm
0.0393701
inches, in
inches, in
0.0254
meters, m
39.3701
inches, in
feet, ft
0.3048
meters, m
3.280840
feet, ft
yards, yd
0.9144
meters, m
1.09361
yards, yd
miles, mi
1.609344
kilometers, km
0.621371
miles, MI
Area
square inch, in2, si
645.16
square millimeters, mm2
0.00155000
square inch, in2
square inch, in2, si
0.00064516
square meter, m2
1550.00
square inch, in2
square feet, ft2, sf
0.09290304
square meter, m2
10.7639
square feet, ft2, sf
square yard, yd2, sy
0.836127
square meter, m2
1.19599
square yard, yd2

Volume

cubic inch, in3, ci
16387.064
cubic millimeters, mm3
61.0237 x 10-6
cubic inch, in3
cubic inch, in3, ci
16.387064
cubic centimeters, cc, cm3
0.06102374
cubic inch, in3
cubic foot, ft3, cf
0.0283168
cubic meters, m3
35.3147
cubic foot, ft3, cf
cubic yard, yd3, cy
0.764555
cubic meters, m3
1.30795
cubic yard, yd3
gallon, gal.
3.78541

Liters, l = 0.001 m3

0.264172
gallon, gal.
Other Geometric Properties of a Cross-section
Moment of Inertia, in4
416231
mm4 = 10-12 m4
2.402 x 10-6
in4
Section Modulus, in3
16387.064
mm3 = 10-9 m3
61.0237 x 10-6
in3

Excerpts/adaptions from: Aluminum Design Manual, Aluminum Association, Inc., October, 1994, Table A1-1, pg. Appendix 1-4. Underlined values units represent an "exact" conversion factor.

- Top - Geometric Conversions - Force and Stress Conversions - Same System Conversions -
- Pounds, Newtons & Kilograms;  Density - Temperature -


4b. Force, Stress, Loads and Mass - English Units to S.I. Units and Back

To Convert From
multiply
to get / To Convert from
multiply by
to get
Force
pound, lb
4.44822
newton, N
0.224809
lb
kilopound, kip = 1000 lb
4.44822
kilonewton, kN = 1000 N
0.224809
kip = 1000 lb
Stress [Force per Unit Area]
pounds per sq. ft, lb/ft2, psf
47.8803
pascals, Pa = N/m2
0.0208854
lb/ft2, psf
psf
0.0478803
kilopascal, kPa, kN/m2
20.8854
psf
kilopounds per sq. ft, ksf
47.8803
kPa
0.0208854
ksf
pounds per sq. inch, psi
6894.76
Pa
0.000145038
psi
psi
6.89476
kPa
0.145038
psi
kilopounds per sq. in, ksi
6.89476
megapascal, MPa
= MN/m2 = N/mm2
0.145038
ksi
Bending Moment, Torque [Force x Length]
pound-foot, lb-ft
1.35582
newton-meter, N-m
0.737561
lb-ft
pound-inch, lb-in
0.112985
N-m
8.850732
lb-in
Distributed (or "Running") Load [Force per Unit Length]
pounds per (linear) foot, plf
14.5939

newtons per meter, N/m

0.06852178
plf
pounds per (linear) inch, pli
175.127
N/m
0.00571015
pli

Excerpts/adapted from: Aluminum Design Manual, Aluminum Association, Inc., October, 1994, Table A1-2, pg. Appendix 1-4.

- Top - Geometric Conversions - Force and Stress Conversions - Same System Conversions -
- Pounds, Newtons & Kilograms;  Density - Temperature -


4c. Same System Conversions; Things you should know

From
Multiply by
to get / To Convert from
multiply by
to get
Length
in
0.083333
feet, ft
12
in
ft
0.333333
yards, yd
3
ft
ft
1.89393 x10-4
miles, MI
5280
feet, ft
mm
0.001
meters, m
1000
mm
cm
0.01
m
100
cm
Area
in2
0.00694444
ft2
144
in2
ft2
0.111111
yd2
9
ft2
Time
second, s
0.0166666
minutes, min
60
s
second
2.77777 x10-4
hour, h
3600
s
second
1.1574 x 10-5
day, d
86400
s
minutes, min
6.9444 x10-4
day,d
1440
min
Weight
lb
0.005
ton (U.S.)
2000
lb

- Top - Geometric Conversions - Force and Stress Conversions - Same System Conversions -
- Pounds, Newtons & Kilograms;  Density - Temperature -


4d. Force and Weight; and Density - English Units to S.I. Units and Back

In the S.I. system, weight is often expressed in kilograms (a mass); in the United States, weight is expressed in pounds (a force). Be careful! The force of 1 kg. is 9.81 N (in standard gravity).

To Convert From
Multiply by
to get / To Convert from
multiply by
to get
Pounds, Newtons and Kilograms
pounds lb
4.44822
Newton, N
0.224809
lb
lb
0.453592
kg
2.20462
lb
N
0.101972
kg
9.80665
N
lb
0.0310
slug (lb-s2/ft)
32.2
lb
Weight Density (force/volume); including kilogram force
lb / ft3
0.157087
kilonewtons per kN/m3
6.36590
lb / ft3
lb / in3
271.447
kN/m3
0.00368
lb / in3
lb / in3
0.000578703
lb / ft3
1728
lb / in3
N / m3
0.101972
kg / m3
9.80665
N / m3
kN / m3
101.972
kg / m3
0.0090665
kN / m3
lb / ft3
16.0185
kg / m3
0.0624279
lb / ft3
Mass Density (mass/volume)
slug / ft3
515.379
kg / m3
0.0019403
slug / ft3

- Top - Geometric Conversions - Force and Stress Conversions - Same System Conversions -
- Pounds, Newtons & Kilograms;  Density - Temperature -


4e. Temperature Conversions

To Convert From
function
to get / To Convert from
function
to get
degrees Fahrenheit, F
(5/9)(F-32)
degrees Centigrade C
1.8 C + 32
degrees Fahrenheit, F
deg. F
F+459.67
degrees Rankine, R
R-459.67
deg. F
deg. Centigrade
C+273.15
Kelvin, K
K-273.15
deg. Centigrade
change in degrees F (or R)
(5/9)(DF)
change in deg. C (or K)
1.8(DC)
change in deg. F.

- Top - Geometric Conversions - Force and Stress Conversions - Same System Conversions -
- Pounds, Newtons & Kilograms;  Density - Temperature -


Elastic Constants - Strength - Density & Thermal Coefficients - Unit Conversions Tables