Specific weight

Not to be confused with Specific gravity, Specific density, or Specific force.

The specific weight, also known as the unit weight (symbol γ, the Greek letter gamma), is a volume-specific quantity defined as the weight per unit volume of a material.

A commonly used value is the specific weight of water on Earth at 4 °C (39 °F), which is 9.807 kilonewtons per cubic metre or 62.43 pounds-force per cubic foot.<ref name="FE">National Council of Examiners for Engineering and Surveying (2005). Fundamentals of Engineering Supplied-Reference Handbook (7th ed.). ISBN 1-932613-00-5. </ref>

Definition

The specific weight, γ, of a material is defined as the product of its density, ρ, and the standard gravity, g: <math display=block>\gamma = \rho \, g</math>

The density of the material is defined as mass per unit volume, typically measured in kg/m³. The standard gravity is acceleration due to gravity, usually given in m/s², and on Earth usually taken as 9.81 m/s².

Unlike density, specific weight is not a fixed property of a material. It depends on the value of the gravitational acceleration, which varies with location. Pressure may also affect values, depending upon the bulk modulus of the material, but generally, at moderate pressures, has a less significant effect than the other factors.<ref name="fluids" />

Applications

Fluid mechanics

In fluid mechanics, specific weight represents the force exerted by gravity on a unit volume of a fluid. For this reason, units are expressed as force per unit volume (e.g., N/m³ or lbf/ft³). Specific weight can be used as a characteristic property of a fluid.<ref name="fluids" />

Soil mechanics

Specific weight is often used as a property of soil to solve earthwork problems.

In soil mechanics, specific weight may refer to:

Moist unit weight

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Dry unit weight

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Saturated unit weight

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Submerged unit weight

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Civil and mechanical engineering

Specific weight can be used in civil engineering and mechanical engineering to determine the weight of a structure designed to carry certain loads while remaining intact and remaining within limits regarding deformation.

Specific weight of water

See also: Water density

Specific weight of water at standard sea-level atmospheric pressure (Metric units) <ref name="fluids" />

Temperature(°C)	Specific weight (kN/m3)
0	9.805
5	9.807
10	9.804
15	9.798
20	9.789
25	9.777
30	9.765
40	9.731
50	9.690
60	9.642
70	9.589
80	9.530
90	9.467
100	9.399

Specific weight of water at standard sea-level atmospheric pressure (English units) <ref name="fluids">Finnemore, J. E. (2002). Fluid Mechanics with Engineering Applications. New York: McGraw-Hill. ISBN 0-07-243202-0.</ref>

Temperature(°F)	Specific weight (lbf/ft3)
32	62.42
40	62.43
50	62.41
60	62.37
70	62.30
80	62.22
90	62.11
100	62.00
110	61.86
120	61.71
130	61.55
140	61.38
150	61.20
160	61.00
170	60.80
180	60.58
190	60.36
200	60.12
212	59.83

Specific weight of air

Main article: Density of air

Specific weight of air at standard sea-level atmospheric pressure (Metric units) <ref name="fluids" />

Temperature(°C)	Specific weight (N/m3)
−40	14.86
−20	13.86
0	12.68
10	12.24
20	11.82
30	11.43
40	11.06
60	10.4
80	9.81
100	9.28
200	7.33

Specific weight of air at standard sea-level atmospheric pressure (English units) <ref name="fluids" />

Temperature(°F)	Specific Weight (lbf/ft3)
−40
−20	0.0903
0	0.08637
10	0.08453
20	0.08277
30	0.08108
40	0.07945
50	0.0779
60	0.0764
70	0.07495
80	0.07357
90	0.07223
100	0.07094
120	0.06849
140	0.0662
160	0.06407
180	0.06206
200	0.06018
250	0.05594

External links

• Submerged weight calculator
• Specific weight calculator
• http://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.html
• http://www.themeter.net/pesi-spec_e.htm