Where the 1,000 Comes From
Both units are SI. The kilogram per cubic meter is the coherent SI unit of density — mass in kilograms over volume in cubic meters. The gram per cubic centimeter is the same quantity expressed in smaller units: a gram is 1/1,000 of a kilogram, and a cubic centimeter is 1/1,000,000 of a cubic meter. Divide those two fractions and the 1,000s cancel into a clean factor: 1 g/cm³ = 1,000 kg/m³, exactly, with no measured constant involved. This is a definitional conversion — the kind this site labels "exact" without any metrology caveat.
The same logic explains why water sits at the memorable value of 1. The gram was originally defined, in 1795, as the mass of one cubic centimeter of water at its maximum density — which made water exactly 1 g/cm³ by construction, and therefore exactly 1,000 kg/m³. Seawater, at about 1.025 g/cm³, is 1,025 kg/m³. Every material's density in g/cm³ is a number you can compare directly to water — which is where the concept of specific gravity comes from, since specific gravity is just density divided by water's density.
g/cm³ = kg/m³ ÷ 1,000
because 1 g/cm³ = 1,000 kg/m³ — exact SI definition
Divide by 1,000, or move the decimal three places left.
Common kg/m³ to g/cm³ Conversions
| kg/m³ | g/cm³ | Material |
|---|---|---|
| 1 kg/m³ | 0.001 g/cm³ | The definitional anchor. |
| 1.225 kg/m³ | 0.001225 g/cm³ | Air at sea level (15 °C). |
| 100 kg/m³ | 0.1 g/cm³ | Light foam insulation. |
| 600 kg/m³ | 0.6 g/cm³ | Dry pine wood. |
| 917 kg/m³ | 0.917 g/cm³ | Ice — floats on water. |
| 1,000 kg/m³ | 1 g/cm³ | Water at 4 °C — the reference. |
| 1,025 kg/m³ | 1.025 g/cm³ | Seawater. |
| 1,360 kg/m³ | 1.36 g/cm³ | Mercury's lighter cousin, bromine. |
| 2,700 kg/m³ | 2.7 g/cm³ | Aluminum — the most common metal shorthand. |
| 7,850 kg/m³ | 7.85 g/cm³ | Carbon steel. |
| 8,960 kg/m³ | 8.96 g/cm³ | Copper. |
| 13,600 kg/m³ | 13.6 g/cm³ | Mercury. |
| 22,590 kg/m³ | 22.59 g/cm³ | Osmium — the densest natural element. |
Worked Examples
Aluminum from datasheet to FEA model
A 6061 aluminum datasheet lists density 2.70 g/cm³. The FEA software needs kg/m³: 2.70 × 1,000 = 2,700 kg/m³. That 2,700 goes into the material definition, and the model's weight output is only as good as this conversion. If the engineer types 2.70 into the kg/m³ field by mistake, the model underweights every aluminum part by a factor of 1,000 — a parts list that shows grams instead of kilograms, and a structure that fails its load checks in the review.
Air density in both units
Air at sea level and 15 °C has a density of about 1.225 kg/m³. In g/cm³: 1.225 ÷ 1,000 = 0.001225 g/cm³ — a number small enough that nobody uses g/cm³ for air. The choice of unit tells you the field: g/cm³ for solids, kg/m³ for liquids and gases, lb/ft³ for US construction. The conversion between the two is always the same exact 1,000, regardless of which material you're describing.
Mercury's dramatic number
Mercury's density is 13.6 g/cm³ — a number so distinctive it's almost a party trick. In kg/m³: 13,600. A barometer's mercury column works because mercury is 13.6× denser than water, so a 760 mm column balances 10.3 m of water. The density conversion underlies the entire pressure-family connection — and if you're converting pressure, the pressure converters on this site carry the same mercury-based constants.
Engineering Context
Density sits between the mass and volume families — it's their ratio. The kg/m³↔g/cm³ conversion is exact because both units are SI; the same 1,000 appears when you realize a cubic meter holds exactly 1,000 liters, which is why water is also 1 kg/L — the liters to mL and kg to g converters both feed into this page's logic. For the US customary side of density — pounds per cubic foot — see the kg/m³ to lb/ft³ converter, which carries the 1959 treaty constants this page doesn't need. The density hub collects all ten converters.
More: g/cm³ to kg/m³ · kg/m³ to lb/ft³ · g/cm³ to lb/ft³ · kg/m³ to g/L · Density Guide
Related Unit Converters
Frequently Asked Questions
Is g/cm³ the same as g/mL?
Yes, exactly — 1 cm³ = 1 mL by definition. The milliliter was defined as one cubic centimeter, so a density expressed in g/cm³ has the identical numerical value in g/mL. Water is 1 g/cm³ = 1 g/mL = 1,000 kg/m³. The g/L form on this site's kg/m³ to g/L page is one more decimal place of the same ladder.
Why does density get cubed errors?
Because density is mass per unit volume, and volume is a length cubed. When you convert a density between systems that use different length units — say, SI to US customary — the length conversion factor gets applied three times. A 1% error in a length factor becomes a 3% error in density. This is why the constants on this page are exact: there's no room for rounding in a quantity that magnifies unit error.
What is specific gravity and how does it relate?
Specific gravity is density divided by the density of water — a dimensionless ratio. Since water is 1 g/cm³ = 1,000 kg/m³, a material's specific gravity is numerically equal to its density in g/cm³. Aluminum: 2.7 g/cm³, specific gravity 2.7. That's why g/cm³ feels so natural: it's one decimal away from specific gravity, the number every diver, brewer, and materials engineer actually reasons with.