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The S.I. and English Systems
The System International (International Standard System) use newtons (N) and meters (m) for its units of
force and length. The U.S.Customary System (English, imperial, engineering system) uses
pounds (lb) and feet (ft) or inches (in.).
The unit of time, seconds (s, sec) is the same in both systems.
Below are tables that convert units from USCS 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 answers need
not be that precise).
Online resources. A useful interactive conversion tool, with many more units,
is Engineering Exchange's Unit
Conversion widget. Another tool, Convert, by Joshua Madison, may be downloaded
here (remember, pressure has the same units
as stress).
| Some approximate (within 2%) conversions useful in engineering mechanics (i.e., statics, dynamics, strength of materials): |
- 1 lb - 4.5 N
- 1 in. = 25 mm
- 1 m ~ 40 in. ~ 3.25 ft
- 1 ksi ~ 7 MPa (1 psi ~ 7 kPa); multiply by 7 and increase prefix by 3 order of magnitude
|
4a. Lengths, Areas and Volumes -
English Units to S.I. Units and Back
Underlined values represent an exact conversion factor.
|
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 |
| 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 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
|
| 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 (SI), sec (US) |
0.0166666
|
minutes, min
|
60
|
s, sec |
| second |
2.77777 x10-4
|
hour, h
|
3600
|
s, sec |
| second |
1.1574 x 10-5
|
day, d
|
86400
|
s, sec |
| minutes, min |
6.9444 x10-4
|
day,d
|
1440
|
min |
| Weight |
| lb |
0.005
|
ton (U.S.)
|
2000
|
lb |
| lb |
0.0025 |
kips (U.S.) |
1000 |
lb |
| Top | Geometric
Conversions | Force and Stress Conversions
|
|
Same System Conversions
| Pounds, Newtons & Kilograms; Density
| Temperature |
4d. Force, Weight and Density - English Units
to S.I. Units and Back
Caution! In the S.I. system, "weight" is often expressed in kilograms (or kilogram-force, kgf). One (1.0) kgf is the force required to accelerate 1.0 kg mass by 1.0 m/s2. "Weight" given in kilograms must be converted to force: the weight of 1.0 kg mass 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 |
| kilopounds, kips |
4.44822
|
kilonewton, kN
|
0.224809
|
kips |
| 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 (kgf) |
| 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,
|
use function
|
to get / To Convert from
|
use function
|
to get
|
| degrees fahrenheit, °F |
(5/9)(F – 32)
|
degrees centigrade, °C
|
1.8 C + 32
|
degrees fahrenheit, °F |
| °F |
F + 459.67
|
degrees Rankine, R
|
R – 459.67
|
°F |
| degrees centigrade, °C |
C + 273.15
|
degrees Kelvin, K
|
K – 273.15
|
°C |
| change in °F (or R) |
(5/9)(D°F)
|
change in deg. °C (or K)
|
1.8(D°C)
|
change in °F (or R) |
| Top | Geometric Conversions | Force and Stress Conversions |
| Same System Conversions | Pounds, Newtons & Kilograms; Density | Temperature |
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