Density Converter
Convert density between kg/m³, g/cm³, g/mL, kg/L, g/L, lb/ft³, lb/in³, oz/in³ and pounds per US gallon.
Updated Formula covered by automated tests
Density tells you how much mass sits in a given volume, and it is the number behind questions like how heavy a tank of fuel is, whether a block of metal is aluminum or steel, or how many truckloads a pile of gravel will fill. Material data sheets give it in kilograms per cubic meter or grams per cubic centimeter, US construction and machining references use pounds per cubic foot or per cubic inch, and fuel and chemical suppliers often quote pounds per gallon. This converter shows a density in all of those units together.
Several of the metric units are numerically identical, which is handy once you notice it: grams per cubic centimeter, grams per milliliter and kilograms per liter are the same unit, and one of them equals 1000 kg/m³. Water near room temperature is close to 1 g/cm³, so a density in g/cm³ doubles as a rough specific gravity.
The formula
- ρ
- Density (the Greek letter rho), mass per unit volume
- m
- Mass of the sample, in kilograms, grams or pounds
- V
- Volume the sample occupies, in cubic meters, liters, cubic feet, cubic inches or gallons
- 0.028316846592 m³
- One cubic foot, from the exact foot of 0.3048 m cubed
- 231 in³
- One US liquid gallon, by definition, which is 3.785411784 L
Because density is a ratio, every conversion factor is a mass factor divided by a volume factor. The pound is defined as exactly 0.45359237 kg and the inch as exactly 2.54 cm, so all of the US customary density units here are exact multiples of kg/m³ even though the decimals look untidy. A cubic foot holds 12³ = 1728 cubic inches, which is why lb/in³ values are 1728 times larger than lb/ft³ values for the same material.
The liter was redefined in 1964 as exactly one cubic decimeter, which is what makes g/mL and g/cm³ interchangeable today. Older references from before that date used a liter slightly larger than a cubic decimeter, but the difference (about 28 parts per million) matters only in precision metrology.
Worked example
Rosa is pricing aluminum plate from a US supplier whose catalog lists weights in pounds, while her alloy data sheet gives a density of 2.70 g/cm³. She needs the density in lb/in³ to estimate part weights from CAD volumes.
- 1 Convert to SI: 2.70 g/cm³ × 1000 = 2700 kg/m³.
- 2 Convert to pounds per cubic foot: 2700 ÷ 16.018463 = 168.56 lb/ft³.
- 3 Convert to pounds per cubic inch: 168.56 ÷ 1728 = 0.09754 lb/in³.
- 4 Check a part: a 12 in × 12 in × 0.25 in plate is 36 in³, so it weighs 36 × 0.09754 = 3.51 lb.
Result: Aluminum at 2.70 g/cm³ is 168.6 lb/ft³ or about 0.0975 lb/in³, so a one-foot-square quarter-inch plate weighs about 3.5 lb.
Before you rely on the result
- Densities of gases, liquids and many solids depend on temperature and pressure; a converted value is only as good as the conditions under which the original figure was measured.
- Bulk materials such as soil, gravel, flour or powder have a bulk density that includes air gaps and varies with compaction, which can differ greatly from the density of the solid grains.
Frequently asked questions
What is the density of water in lb/ft³ and lb/gal?
At about 1000 kg/m³, water is 62.43 lb/ft³ and 8.345 lb per US gallon. The exact value depends on temperature: pure water peaks near 999.97 kg/m³ at about 4 °C and is about 998.2 kg/m³ at 20 °C.
How is specific gravity related to density?
Specific gravity is the density of a substance divided by the density of water, so it has no unit. A liquid with specific gravity 0.8 has a density of about 0.8 g/cm³ or 800 kg/m³, provided the reference water temperature is stated or close to room temperature.
Why does fuel density change with temperature?
Liquids expand when they warm, so the same mass takes up more volume and the density falls. Fuel is therefore often traded at a reference temperature (15 °C in much of the world, 60 °F in the US) so that a liter or gallon means the same mass everywhere.
Are kg/L and g/cm³ really the same?
Yes. One liter is 1000 cm³ and one kilogram is 1000 g, so the factors of 1000 cancel. A value of 0.92 kg/L, typical of olive oil, is also 0.92 g/cm³, 0.92 g/mL and 920 kg/m³.