Density Converter
Enter a density and its unit, and pick the unit to convert to. The table shows the density in every unit, and the specific gravity compares it with water at 1 g/cm³.
Converted density
62.427961 lb/ft³
Specific gravity (relative to water)
1
How it works
Density is mass per volume, so converting it means converting a mass unit and a volume unit at once. Every value is first expressed in kilograms per cubic metre, the SI unit, then divided by the size of the unit you are converting to. The factors come from the exact definitions of the pound (0.45359237 kg), the inch (25.4 mm) and the US gallon (231 cubic inches).
Several common units are the same size under different names: 1 g/cm³ = 1 g/mL = 1 kg/L = 1,000 kg/m³, and 1 g/L = 1 kg/m³. Pounds per cubic foot and pounds per US gallon are the usual US customary units for bulk materials and liquids; pounds per cubic inch appears in engineering tables for metals.
Specific gravity is the density divided by the density of water, taken here as 1,000 kg/m³ (1 g/cm³), the conventional reference. It is dimensionless, so a material with specific gravity 2.4 is 2.4 times as dense as water whatever unit you measure in, and it floats if its specific gravity is below 1.
Formula
kg/m³ = value × kg/m³ per source unit converted = kg/m³ ÷ kg/m³ per target unit 1 g/cm³ = 1,000 kg/m³; 1 g/L = 1 kg/m³ 1 lb/ft³ = 0.45359237 ÷ 0.3048³ = 16.018463 kg/m³ 1 lb/in³ = 0.45359237 ÷ 0.0254³ = 27,679.905 kg/m³ 1 lb/US gal = 0.45359237 ÷ (231 × 0.0254³) = 119.826427 kg/m³ specific gravity = density in kg/m³ ÷ 1,000
Example
Water at 1 g/cm³, the default, is 1,000 kg/m³, which is 1,000 ÷ 16.018463 = 62.427961 lb/ft³. It is also 8.345404 lb per US gallon and 0.036127 lb/in³, and its specific gravity is 1 by definition.
Mild steel at 7.85 g/cm³ is 7,850 kg/m³ = 490.06 lb/ft³, specific gravity 7.85. Air at sea level, 1.225 kg/m³, is 0.0765 lb/ft³ with specific gravity 0.001225.
Assumptions and limitations
- Specific gravity uses 1,000 kg/m³ for water, the conventional reference (water's actual maximum density is 999.97 kg/m³ at 3.98 °C, and 998.2 kg/m³ at 20 °C). Standards that specify a reference temperature, such as API gravity at 60 °F, differ by that much.
- The pound is the avoirdupois pound (0.45359237 kg) and the gallon the US liquid gallon (231 in³). An imperial gallon is 4.54609 L, so a lb per imperial gallon is 0.8327 lb per US gallon.
- The converter changes units only; it does not correct a density for temperature or pressure.
- Results are shown to six decimal places; the underlying arithmetic is double precision.
Frequently asked questions
What are some common densities for reference?
Water 1.00 g/cm³ (1,000 kg/m³, 62.4 lb/ft³) at 4 °C; seawater about 1.025 g/cm³; ice 0.917 g/cm³; concrete about 2.4 g/cm³ (150 lb/ft³); aluminium 2.70 g/cm³; mild steel 7.85 g/cm³ (490 lb/ft³); lead 11.34 g/cm³; gold 19.3 g/cm³; dry air at sea level 1.225 kg/m³. These are typical values from the CRC Handbook of Chemistry and Physics and engineering tables; alloys, mixes and temperature change them.
Is g/mL the same as g/cm³?
Yes. A millilitre is defined as one cubic centimetre, so g/mL and g/cm³ are the same unit, and so is kg/L. Use the g/cm³ row for any of them.
How many pounds does a gallon of water weigh?
About 8.34 lb. Water at 1 g/cm³ is 8.345404 lb per US gallon; at room temperature it is a little less, about 8.33 lb. An imperial gallon of water weighs about 10 lb.
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