Density Unit Converter
Density is mass per unit volume. The SI unit is kg/m3, but engineers and scientists work with many other density units depending on context. This converter handles kg/m3, g/cm3 (the most common in chemistry), lb/ft3 (US construction and materials), lb/in3 (metals and precision engineering), and lb/US gallon (paints, coatings, and drilling fluids). All factors are derived from the exact NIST definitions of the US gallon, foot, and pound.
Density conversion factors (referenced to kg/m3)
1 g/cm3 = 1,000 kg/m3 | 1 lb/ft3 = 16.0185 kg/m3 | 1 lb/gal = 119.826 kg/m3
Key reference: water = 1,000 kg/m3 = 1.000 g/cm3 = 62.428 lb/ft3 = 8.3454 lb/US gal at 4 C. Conversion factors use exact NIST-defined constants: 1 lb = 0.45359237 kg, 1 ft = 0.3048 m, 1 US gal = 3.785411784 L.
Density reference values
- Air at STP: 1.225 kg/m3.
- Water at 4 C: 1,000 kg/m3 = 1.000 g/cm3.
- Aluminum: 2,700 kg/m3 = 2.70 g/cm3.
- Steel: 7,850 to 8,000 kg/m3.
- Copper: 8,940 kg/m3.
- Gold: 19,300 kg/m3.
Density unit converter: frequently asked questions
How do I convert kg/m3 to g/cm3?
Divide kg/m3 by 1,000 to get g/cm3. Since 1 kg = 1,000 g and 1 m3 = 1,000,000 cm3, the ratio is 1,000 g / 1,000,000 cm3 = 0.001 g/cm3 per kg/m3. Water at 4 C has a density of 1,000 kg/m3 = 1.000 g/cm3.
What is the density of water?
Water has its maximum density at 4 degrees Celsius: approximately 999.97 kg/m3, or 1.000 g/cm3. At 20 C it is 998.2 kg/m3. Saltwater is denser, approximately 1,025 kg/m3.
How is pounds per gallon used?
Pounds per US gallon (lb/gal) is used in the US for liquids such as paint, chemicals, and drilling muds. One lb/gal = 119.826 kg/m3. Water weighs approximately 8.34 lb/gal.
What is the difference between specific gravity and density?
Specific gravity is dimensionless: it is the ratio of a substance's density to the density of water at 4 C (1,000 kg/m3). Because the reference density is 1 g/cm3, specific gravity equals the numerical value of density in g/cm3 units.
What is kg/L and how does it compare to g/cm3?
Kilogram per liter (kg/L) is identical in value to g/cm3 because 1 liter = 1 dm3 = 1,000 cm3 and 1 kg = 1,000 g, so 1 kg/L = 1,000 g / 1,000 cm3 = 1 g/cm3. Water is 1.000 kg/L = 1.000 g/cm3 at 4 C.
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units (SI).
- NIST Handbook 44: US units of measure.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.