Density Converter
What this converter does
Density tells you how much mass occupies a given volume. Material data sheets, fuel specifications, water-treatment reports and shipping documents often quote the same property in different units: kilograms per cubic metre in an SI table, grams per cubic centimetre in a laboratory note, pounds per US gallon on a chemical label. This page converts one stated density into another unit. It does not measure or estimate the density of a material for you.
How the conversion works
Every unit is first converted to the SI coherent unit, kilograms per cubic metre (kg/m³), and then to the target unit. Each factor below states how many target units equal 1 kg/m³:
| Unit | Amount equal to 1 kg/m³ |
|---|---|
| g/cm³ = kg/L = t/m³ | 0.001 |
| g/L | 1 |
| mg/L | 1,000 |
| g/m³ | 1,000 |
| lb/ft³ | 0.0624279606 |
| lb/in³ | 0.0000361273 |
| lb/gal (US) | 0.0083454045 |
| lb/gal (UK) | 0.0100224129 |
| oz/ft³ | 0.9988473692 |
| slug/ft³ | 0.0019403203 |
| long ton/yd³ | 0.0007524799 |
The customary factors are derived from exact legal definitions rather than rounded look-up values: 1 lb = 0.45359237 kg, 1 ft = 0.3048 m, 1 US gallon = 3.785411784 L and 1 UK gallon = 4.54609 L. The slug is taken as 1 lbf·s²/ft, or about 14.5939 kg. A useful mental check is that 1 g/cm³ is exactly 1,000 kg/m³ and roughly 62.43 lb/ft³.
Worked example
A structural steel specification lists a density of 7,850 kg/m³. Dividing by 1,000 gives 7.85 g/cm³. Multiplying by 0.0000361273 gives 0.2836 lb/in³, the figure a US machining handbook would use to estimate the mass of a billet from its dimensions.
Second case: a seawater sample is reported as 1.03 kg/L. That is 1,030 kg/m³, and 1,030 × 0.0083454 = 8.596 lb per US gallon. Using the UK gallon instead would give about 10.32 lb/gal, which is why the gallon definition must always be named.
What the result means
The converted number describes the same physical density; only the unit has changed. If you convert 7.85 g/cm³ to lb/ft³ and back, you should recover 7.85 apart from display rounding. A result that differs by a factor of exactly 1,000 usually means kg/L was confused with kg/m³, and a factor near 1.2 usually signals that US and UK gallons were mixed.
Accuracy and limitations
- Density depends on temperature and, for gases and compressible liquids, on pressure. A converted value remains valid only for the conditions stated with the original measurement.
- The page performs unit arithmetic only. It is not a material database and should not replace a certified value from a supplier or test report.
- Bulk density of powders, soils or grain includes voids and packing; it is not interchangeable with the particle density of the same material.
- Results are shown to about ten significant digits; round to the precision of your source data before reporting them.
Sources
- BIPM SI Brochure — definitions of coherent SI units, including kilogram per cubic metre.
- NIST SP 811 Appendix B.9 — conversion factors grouped by physical quantity.
- NIST SP 811 Appendix B.8 — exact definitions of the pound, foot, inch and gallon.
Editorial record
Written and reviewed by the SoupCalc Editorial Team. Last reviewed: September 25, 2026.