Density Converter
Convert between kg/m³, g/cm³, lb/ft³, kg/L, and other density units.
Density Converter
Enter a density value and select its unit — all other units update instantly.
Material Densities
How to Convert Between Kg/m³, G/cm³, Lb/ft³, and Specific Gravity
A concrete specification calls for 150 lb/ft³ aggregate. Your supplier quotes in kg/m³. Type 150, select lb/ft³, and see that it equals 2,403 kg/m³, 2.403 g/cm³, and 2.403 SG. The material reference section confirms normal-weight concrete is around 2,400 kg/m³, so the numbers match.
The converter handles 11 units: kg/m³, g/cm³, g/mL, kg/L, g/L, lb/ft³, lb/in³, lb/US gal, lb/imp gal, specific gravity, and slug/ft³. A food scientist measuring honey at SG 1.42 sees it equals 1,420 kg/m³ and 88.6 lb/ft³. A chemical engineer working with ethanol at 0.789 g/cm³ sees it equals 789 kg/m³ and 49.3 lb/ft³. The material reference shows air at 1.225 kg/m³ to osmium at 22,590 kg/m³.
Why density units confuse engineers across borders
A US-designed chemical plant specifies a fluid at 62.4 lb/ft³. The European team needs kg/m³. The conversion factor is 16.0185: 62.4 x 16.0185 = 1,000 kg/m³ (water). If the engineer mistakenly uses 62.4 kg/m³ instead of 1,000, the pipe sizing is wrong by a factor of 16, and the pump cannot deliver the required flow rate.
Specific gravity (SG) is dimensionless: the ratio of a substance density to water density (1,000 kg/m³ at 4°C). Gold at SG 19.3 means 19.3x denser than water. A jeweller verifying gold purity measures SG: 19.3 = pure, 18.0 = 14-karat alloy. SG works because it is the same number in any unit system.
A lab technician measures a polymer at 1.15 g/mL. The factory specification requires kg/m³. Since 1 g/mL = 1,000 kg/m³, the polymer is 1,150 kg/m³. If the technician reports 1.15 kg/m³ (forgetting the factor of 1,000), the factory rejects the batch as too light. The converter prevents this error.
How the Density Converter Handles Kg/m³, G/cm³, and Lb/ft³
All conversions pass through kilograms per cubic meter (kg/m³). When you enter 8.96 g/cm³ (copper), the tool multiplies by 1,000 to get 8,960 kg/m³. Then it divides by each target unit's factor: by 16.0185 for lb/ft³, by 1,000 for specific gravity, by 0.03613 for lb/in³. The result: 8.96 g/cm³ = 8,960 kg/m³ = 559.1 lb/ft³ = 8.96 SG.
Why g/cm³ and kg/m³ differ by exactly 1,000
1 g/cm³ = (0.001 kg) / (0.000001 m³) = 1,000 kg/m³. This factor of 1,000 comes from the centi prefix (10^-2) cubed: (10^-2)^3 = 10^-6 for volume, and the kilo prefix (10^3) for mass. The same factor applies to g/mL and kg/L since 1 mL = 1 cm³ and 1 L = 1,000 cm³. This is why specific gravity (which compares to water at 1,000 kg/m³) numerically equals g/cm³.
Imperial conversion factors from exact definitions
lb/ft³ = 16.0185 kg/m³, derived from 1 lb = 0.45359237 kg and 1 ft = 0.3048 m. So 1 lb/ft³ = 0.45359237 / (0.3048)^3 = 0.45359237 / 0.0283168 = 16.0185. The US gallon factor is 8.3454 lb/US gal (from 1 US gal = 3.78541 L and water density). The imperial gallon factor is 10.022 lb/imp gal (from 1 imp gal = 4.54609 L). The slug is 14.5939 kg, derived from 1 lbf = 4.44822 N and g = 9.80665 m/s².
Specific gravity is dimensionless: the ratio of a substance density to water density at 4°C (1,000 kg/m³). So SG = density in kg/m³ divided by 1,000. Gold at 19,300 kg/m³ has SG = 19.3. Air at 1.225 kg/m³ has SG = 0.001225. The converter handles SG as a unit with factor 1,000 (since SG x 1,000 = kg/m³).
Frequently Asked Questions
How do I convert 2.7 g/cm³ to lb/ft³?
First convert to kg/m³: 2.7 x 1,000 = 2,700 kg/m³. Then divide by 16.0185: 2,700 / 16.0185 = 168.6 lb/ft³. This is the density of aluminum. The quick shortcut is to multiply g/cm³ by 62.43 to get lb/ft³ directly (since 1,000 / 16.0185 = 62.43). The converter shows all units simultaneously.
What material has a density of 1 g/cm³?
Water at 4°C has a density of exactly 1 g/cm³ = 1,000 kg/m³ = 62.43 lb/ft³ = 1.0 SG. This is why water is the reference standard for specific gravity. Many common materials cluster around this value: wood (0.4-0.8 g/cm³), oil (0.8-0.9 g/cm³), ice (0.917 g/cm³). Materials above 1.0 sink in water, below 1.0 float.
Why does ice float if it is solid water?
Water expands about 9% when it freezes because hydrogen bonding creates an open hexagonal crystal structure. This increases volume while keeping the same mass, reducing density from 1.0 g/cm³ to 0.917 g/cm³. Most materials contract when they solidify and become denser. Water is unusual, and this property is critical for aquatic life because lakes freeze from the top down.
What is the density of common metals?
Aluminum: 2.70 g/cm³ (2,700 kg/m³). Iron: 7.87 g/cm³ (7,870 kg/m³). Copper: 8.96 g/cm³ (8,960 kg/m³). Silver: 10.49 g/cm³ (10,490 kg/m³). Gold: 19.32 g/cm³ (19,320 kg/m³). Osmium: 22.59 g/cm³ (22,590 kg/m³). The density reference section in the converter shows these values for quick lookup.
How accurate is specific gravity for quality control?
Specific gravity is precise to about 0.1% with a standard hydrometer. Honey at SG 1.42 +/- 0.001 indicates about 82% sugar content. Wine at SG 0.995 indicates fermentation is complete (all sugar converted to alcohol). Petroleum products are graded by API gravity, which is a modified specific gravity scale. SG is reliable for quality control because temperature corrections are well-established.
What is the density of air and why does it matter?
Air at sea level and 15°C has a density of 1.225 kg/m³ (0.0765 lb/ft³). This matters for aircraft performance (lift depends on air density), HVAC system sizing (fan capacity depends on air mass flow), and combustion calculations (stoichiometric air-fuel ratio depends on air density). At 3,000 m altitude, air density drops to about 0.91 kg/m³, reducing aircraft lift by 25%.