Density is mass per unit volume, and it explains why a steel bolt sinks while a log floats, why a gallon of gasoline weighs less than a gallon of water, and how many tons of gravel a truck can legally carry. Scientists express it in kilograms per cubic meter or grams per cubic centimeter; American engineers and contractors use pounds per cubic foot, per gallon or per cubic yard. This converter links all 14 units and adds two interpretations: specific gravity and whether the material would float in fresh water.
How to use the density converter
- Enter the density in Value.
- Choose its unit in From and the unit you want in To.
- The tape shows the result, the factors in both directions, the specific gravity and a float-or-sink check.
- The table lists the density in every supported unit.
Density conversion formula
Each unit is defined as a number of kilograms per cubic meter:
Because density combines a mass unit and a volume unit, each factor is built from two exact definitions. For pounds per cubic foot:
Specific gravity is the density divided by that of water, taken here as 1,000 kg/m³:
Worked example: concrete for a slab
Normal-weight concrete has a density of about 2,400 kg/m³. A US ready-mix order is placed in cubic yards, and the truck’s load limit is in pounds:
2,400 kg/m³ ÷ 16.0184634 = 149.83 lb/ft³
2,400 kg/m³ ÷ 0.5932764 = 4,045 lb/yd³
Specific gravity: 2,400 ÷ 1,000 = 2.4, so it sinks.
A 10-cubic-yard truckload therefore carries about 40,450 lb of concrete, which is why mixer trucks often run partially loaded on weight-restricted roads.
Common density conversions
| From | To | Multiply by |
|---|---|---|
| g/cm³ | kg/m³ | 1,000 (exact) |
| g/cm³ | lb/ft³ | 62.427961 |
| lb/ft³ | kg/m³ | 16.018463 |
| g/cm³ | lb/US gal | 8.3454045 |
| lb/US gal | kg/m³ | 119.82643 |
| lb/in³ | g/cm³ | 27.679905 |
| kg/m³ | lb/yd³ | 1.6855549 |
| slug/ft³ | kg/m³ | 515.37882 |
Densities of common materials
| Material | kg/m³ | lb/ft³ | Specific gravity |
|---|---|---|---|
| Air (20 °C, sea level) | 1.204 | 0.0752 | 0.0012 |
| Gasoline | about 745 | 46.5 | 0.745 |
| Ice | 917 | 57.2 | 0.917 |
| Fresh water (20 °C) | 998 | 62.3 | 0.998 |
| Seawater | about 1,025 | 64.0 | 1.025 |
| Concrete | about 2,400 | 149.8 | 2.4 |
| Aluminum | 2,700 | 168.6 | 2.70 |
| Steel | about 7,850 | 490 | 7.85 |
| Gold | 19,320 | 1,206 | 19.32 |
Values for mixtures such as gasoline, concrete and seawater vary with composition and temperature, so treat them as typical rather than exact.
Practical notes
Temperature matters. Most substances expand when warmed, so their density falls. Water is densest at about 4 °C (999.97 kg/m³) and slightly lighter at room temperature, which is why lab data always state a temperature.
Bulk density is not solid density. Gravel, mulch and soil contain air gaps. Crushed stone made of rock with a density of 2,700 kg/m³ may have a bulk density near 1,600 kg/m³ in a pile. Use bulk figures when estimating the weight of a delivery.
Weight per gallon is density in disguise. Paint, fuel and chemicals are often specified in pounds per gallon; this converter turns those into kg/L or specific gravity directly.
To compute density from a measured mass and volume, use the density calculator. For material estimates by weight, see the concrete calculator and the gravel calculator.
Frequently asked questions
How do I convert g/cm³ to kg/m³?
Multiply by 1,000. A cubic meter holds a million cubic centimeters, and a kilogram is a thousand grams, so the factors combine to 1,000. Water at about 1 g/cm³ is 1,000 kg/m³.
What is the density of water in lb/ft³?
About 62.4 lb/ft³ at room temperature (62.43 at its densest, 4 °C). In pounds per US gallon it is about 8.34 lb/gal.
What is specific gravity?
Specific gravity is a material's density divided by the density of water, so it has no units. A specific gravity of 2.7, like aluminum, means the material is 2.7 times as dense as water. Values below 1 float in fresh water.
Are g/cm³ and g/mL the same?
Yes. One milliliter is exactly one cubic centimeter, so a density in g/mL has the same number in g/cm³ and in kg/L.