Density Converters 10
Density is mass divided by volume — which makes it the one conversion on this site that asks you to think in three dimensions before you start. A cubic meter of water weighs 1,000 kg. A cubic foot of water weighs 62.4 lb. The same water, two volumes, two masses, one ratio: 1 g/cm³ = 1,000 kg/m³ = 62.427961 lb/ft³. Every converter here uses exact constants derived from the SI definitions and the 1959 yard/pound agreement — no approximations, because density is where materials science meets money.
Why Density Conversion Bites People
Density is the unit conversion where the numbers look friendly and the physics bites. A materials datasheet says "2.7 g/cm³" — that's aluminum, instantly recognizable. The structural engineer converts it to 2,700 kg/m³ for the FEA model; the US fabricator wants 168.6 lb/ft³ for the weight estimate; the aerospace buyer checks 0.0975 lb/in³ against the aircraft spec. All four numbers describe the same aluminum, and the conversions between them are exact. The trap is the cube: because density multiplies a length by itself twice, any error in the length conversion gets cubed. A 1% error in a unit factor is a 3% error in density — which is why the constants on this page carry full precision.
Density also anchors the "mass → volume → density" triangle this site now covers end to end. The weight & mass page handles the numerator; the volume page handles the denominator; this page combines them. If you know any two of the three — mass, volume, density — you can find the third, and the converters on this page give you the density half of that chain.
What's on this page
Ten converters covering the five density unit families that actually show up in engineering work — kilograms per cubic meter (SI), grams per cubic centimeter (materials science shorthand), pounds per cubic foot (US construction), pounds per cubic inch (aerospace and metals), and grams per liter (water chemistry and solutions). Every factor is exact. The anchors to remember: 1 g/cm³ = 1,000 kg/m³ (a factor of 1,000 — the cube of 10), 1 lb/ft³ = 16.018463 kg/m³ (the 1959 pound over the 1959 foot, cubed), and 1 g/cm³ = 62.427961 lb/ft³. Everything else on this page derives from those three. For the mass side of the ratio, see the weight & mass converters; for the volume side, the volume page; for density in a moving fluid, the speed and frequency families handle the flow side.
Exact conversion factors
Density is the category with the friendliest metric behavior and the least friendly imperial one. Within SI the factors are powers of a thousand; between the systems every factor is built from the pound and the foot.
| From | To | Exact factor | Basis |
|---|---|---|---|
| 1 gram per cubic centimeter | kg per cubic meter | 1,000 | Exact, both are SI |
| 1 gram per liter | kg per cubic meter | 1 | Exact, the thousands cancel |
| 1 kilogram per cubic meter | grams per liter | 1 | Exact |
| 1 pound per cubic foot | kg per cubic meter | 16.018463374 | Exact, 0.45359237 divided by 0.028316846592 |
| 1 pound per cubic inch | kg per cubic meter | 27,679.9047102 | Exact |
| 1 kg per cubic meter | pounds per cubic foot | 0.0624279605761 | Derived, 0.0624279605761 |
| 1 pound per cubic foot | grams per cubic centimeter | 0.016018463374 | Derived, 0.016018463374 |
| 1 gram per cubic centimeter | pounds per cubic foot | 62.4279605761 | Derived, 62.4279605761 |
| 1 pound per cubic inch | grams per cubic centimeter | 27.6799047102 | Derived, 27.6799047102 |
| 1 tonne per cubic meter | kg per cubic meter | 1,000 | Exact, SI prefix |
Defining values and exact constants
- Water is close to 1,000 kg/m³ by construction. The liter was defined as the volume of one kilogram of water at 4 °C, and the modern value is 999.97 kg/m³ at 20 °C.
- Within SI, density needs no factors at all: 1 g/cm³ is 1,000 kg/m³ and 1 g/L is 1 kg/m³, because a cubic meter is a thousand liters and a kilogram a thousand grams.
- One pound per cubic foot is 16.01846337396014 kg/m³. That is 0.45359237 divided by 0.028316846592, both exact definitions.
- One pound per cubic inch is 27,679.904710203 kg/m³, the unit US handbooks use for steel and aluminum sections.
- Handbook values worth memorizing: steel about 7,850 kg/m³, aluminum 2,700, copper 8,960, lead 11,340 and mercury 13,534.
Frequently asked questions
Is 1 g/cm³ the same as 1 kg/m³?
No, it is a thousand times larger. A cubic meter holds a million cubic centimeters and a kilogram is a thousand grams, so the two thousands cancel and leave a factor of 1,000.
Why is 1 g/L equal to 1 kg/m³?
Because both conversions are factors of a thousand pointing in opposite directions. A thousand grams is one kilogram and a thousand liters is one cubic meter, so the ratio is unchanged.
How do you convert lb/ft³ to kg/m³?
Multiply by 16.018463374. Water at 62.4 lb/ft³ is 999.6 kg/m³. The factor is one pound in kilograms divided by one cubic foot in cubic meters.
Does density change with temperature?
Yes, typically by a few tenths of a percent per ten degrees for liquids and much more for gases. Water is densest at 4 °C, which is why ice floats on the water it came from.