Hong Life CalculatorsUnderstanding the density converter — concept and principle
This converter changes a density value between g/cm³, kg/m³, g/L, lb/ft³, lb/in³ and pounds per US gallon. Density tells you how much mass fits into a given volume. Students need it for physics and chemistry problems, engineers and builders for material weights, and cooks, brewers and shippers whenever data comes in metric and imperial units at the same time.
How it is calculated
Density ρ = mass ÷ volume. Converting units means converting the mass unit and the volume unit separately:
- 1 g/cm³ = 1,000 kg/m³ = 1,000 g/L (since 1 m³ = 1,000,000 cm³ and 1 L = 1,000 cm³)
- 1 lb/ft³ = 0.45359237 kg ÷ 0.028316846592 m³ ≈ 16.01846 kg/m³
- 1 lb/in³ ≈ 27.67990 g/cm³
- 1 lb/US gal ≈ 0.1198264 g/cm³ (1 US gallon = 3.785411784 L)
The calculator multiplies your value by the size of the starting unit in g/cm³ and divides by the size of the target unit.
The principle
All of these factors come from exact definitions: the international pound is exactly 0.45359237 kg, the inch exactly 25.4 mm, and the US gallon exactly 231 cubic inches. Because volume is length cubed, a length factor gets cubed too, which is why lb/in³ and lb/ft³ differ by a factor of 1,728 (12³). The metric units are linked by powers of ten: a cube 1 cm on a side holds 1 mL, so 1 g/cm³ is the same as 1 g/mL and 1 kg/L.
Worked example
Default input: 1 g/cm³ to kg/m³.
- 1 g = 0.001 kg and 1 cm³ = 0.000001 m³.
- 1 g/cm³ = 0.001 kg ÷ 0.000001 m³ = 1,000 kg/m³.
- The other units follow the same way: 62.42796058 lb/ft³, 0.036127292 lb/in³ and 8.345404452 lb/US gal.
The calculator shows 1,000 kg/m³, roughly the density of water.
How to read the result
Compare your value with familiar materials (approximate, near room temperature): air about 1.2 kg/m³, ice about 0.92 g/cm³, water about 1.00 g/cm³, aluminium about 2.70 g/cm³, steel about 7.85 g/cm³, gold about 19.3 g/cm³. A material denser than the liquid it is placed in sinks; one less dense floats. Ratio to water is also called specific gravity, which is numerically the density in g/cm³.
Common mistakes
- Forgetting to cube the length factor (1 m³ is 1,000,000 cm³, not 100 cm³).
- Mixing US and UK (imperial) gallons; the imperial gallon is about 4.546 L.
- Treating density as fixed. Liquids and gases change with temperature and pressure; water peaks at about 0.99997 g/cm³ near 4 °C and is about 0.998 g/cm³ at 20 °C.
- Confusing bulk density of powders or soil (with air gaps) with the density of the solid itself.
Frequently asked questions
What is the density of water in lb/ft³?
About 62.4 lb/ft³ (62.43 at its densest near 4 °C).
How do I convert g/cm³ to kg/m³?
Multiply by 1,000. To go back, divide by 1,000.
Are g/mL and g/cm³ the same?
Yes. One millilitre is exactly one cubic centimetre.
Sources: BIPM, The International System of Units (SI Brochure), 9th edition · NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B