How many kg/m³ is 1 g/cm³?
Exactly 1,000 kg/m³. The factor is exact because the metric system's nesting (1 m = 100 cm, 1 kg = 1,000 g) makes the unit ratio clean.
Density calculator
Density converter
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Density is mass per unit volume, indicating how tightly matter is packed. The SI unit is kg/m³. Other common units include g/cm³ (1 g/cm³ = 1,000 kg/m³ exactly), lb/ft³, and lb/in³. Water at 4°C is conveniently 1.000 g/cm³ (the calibration point for the original gram); steel is about 7.85 g/cm³; gold is 19.3 g/cm³.
Example density conversions
1 g/cm³1,000 kg/m³ (exact), 62.428 lb/ft³
1 kg/m³0.001 g/cm³, 0.0624 lb/ft³
1 lb/ft³16.0185 kg/m³
1 lb/in³27,679.9 kg/m³, 27.6799 g/cm³
Open the live density converter for any input value.
Reference densities
Memorable density values that anchor most engineering and physics conversions: water at 4°C is 1,000 kg/m³ or 1.000 g/cm³ exactly (the original gram was defined as the mass of 1 cubic centimeter of water at this temperature). Aluminum is 2.70 g/cm³; steel and iron are 7.8-7.9 g/cm³; copper is 8.96 g/cm³; lead is 11.34 g/cm³; gold is 19.30 g/cm³. Air at sea level is about 1.225 kg/m³, roughly 1/800 of water's density.
These reference points give intuition for unit conversions. If something quotes a density of 'about 7,800 kg/m³', that's steel. '1.2 g/L' is air. '2.7 g/cm³' is aluminum. Comparing a quoted value to these mental anchors catches order-of-magnitude errors quickly.
Specific gravity
Specific gravity (SG) is density expressed as a dimensionless ratio to water at 4°C. Steel's SG is 7.85; gold's is 19.3; gasoline's is 0.74 (it floats). Specific gravity is convenient because it's unit-independent: a substance with SG 0.85 is 0.85 g/cm³ in metric, 850 kg/m³ in SI, or 53 lb/ft³ in US customary. The conversion is the same factor in any unit system.
Brewing, winemaking, and the petroleum industry all use specific gravity heavily. The Brix scale (for sugar content) and the API gravity scale (for petroleum) are derived from specific gravity via simple formulas. For most engineering work, density in kg/m³ or g/cm³ is more direct.
Why density matters in conversions
Converting between mass and volume for a specific substance requires its density. 'How many liters of gasoline is 50 kg?' depends on the density of gasoline (~0.74 g/cm³ at 15°C): 50 kg ÷ 0.74 kg/L ≈ 67.6 L. Recipe-style conversions also require densities: 1 cup of all-purpose flour weighs about 120-125 g because flour's bulk density is about 0.51 g/cm³.
For gases, density changes substantially with temperature and pressure (the ideal gas law: PV = nRT). Air density at sea level is about 1.225 kg/m³ at 15°C, but drops to about 0.40 kg/m³ at 10 km altitude. Liquid densities also change with temperature but more modestly: water density varies by about 4% between 0°C and 100°C.
Common density conversions
| From | Equivalent |
|---|---|
| 1 g/cm³ | 1,000 kg/m³ (exact), 62.428 lb/ft³ |
| 1 kg/m³ | 0.001 g/cm³, 0.0624 lb/ft³ |
| 1 lb/ft³ | 16.0185 kg/m³ |
| 1 lb/in³ | 27,679.9 kg/m³, 27.6799 g/cm³ |
| Water at 4°C | 1.000 g/cm³, 1,000 kg/m³, 62.43 lb/ft³ |
| Air at sea level, 15°C | 1.225 kg/m³, 0.0765 lb/ft³ |
| Aluminum | 2.70 g/cm³, 168.6 lb/ft³ |
| Steel (typical) | 7.85 g/cm³, 490 lb/ft³ |
| Lead | 11.34 g/cm³, 708 lb/ft³ |
| Gold | 19.30 g/cm³, 1,205 lb/ft³ |
Frequently asked questions
What is specific gravity?
Specific gravity is the ratio of a substance's density to water's density at 4°C. It's a dimensionless number; gold's specific gravity is 19.3, water's is 1.0, gasoline's is 0.74. SG is unit-independent, which makes it convenient for cross-system communication.
Why does water have a density of exactly 1.000 g/cm³?
Because the original 1795 gram was defined as the mass of 1 cubic centimeter of water at 4°C. The kilogram was later redefined in terms of a physical artifact and now the Planck constant, so water's density at 4°C is not exactly 1.000 g/cm³ today, but it's accurate to about 5 parts per million, which is more precision than most uses require.
How does density of air compare to water?
Air at sea level is about 1.225 kg/m³; water is 1,000 kg/m³. Water is roughly 815 times denser than air. This is why pressure inside a vacuum chamber doesn't budge a sensitive scale much but submerging a hand-sized object in water displaces noticeable weight.
Why does temperature affect density?
Most materials expand when heated, so their volume increases while mass stays constant, lowering density. Water has an anomaly: its density peaks at 4°C and decreases both above and below that temperature (which is why ice floats). Most engineering density tables specify a reference temperature for this reason.