What is a Density Unit Converter?
The density unit converter switches between kg/m³, g/cm³, and lb/ft³.
How it's calculated
Density = mass ÷ volume
1 g/cm³ = 1,000 kg/m³. Water's density is 1 g/cm³ at 4°C.
Units that are easy to mix up
| Units | Why it's confusing | How to tell them apart |
|---|---|---|
| density vs specific gravity | Both describe "how packed" | Density has units (g/cm³); specific gravity is a unitless ratio to water |
| g/cm³ vs kg/m³ | Numbers differ by 1,000x | 1 g/cm³ = 1,000 kg/m³ — same concept, different scale |
Why water's density is exactly 1
It's not a coincidence — it was defined that way. The metric system was built on the decision that '1 cm³ of water has a mass of 1 gram.' That gives us convenient relationships: 1L of water = 1kg, 1m³ of water = 1,000kg (1 metric ton).
Specific gravity expresses how many times denser something is than water, so because water's density is exactly 1, the number is identical to the g/cm³ value.
Good to know
- Water is densest at 4°C. It becomes lighter as it freezes, which is why ice floats — opposite of most substances, and the reason lakes freeze from the top down, insulating aquatic life below through winter.
- Gold's density is 19.3 g/cm³, far heavier than lead (11.3) — the density difference Archimedes famously used to test whether a crown was pure gold.
- Wood density ranges widely from 0.3 to 1.2 g/cm³, and species like ebony and lignum vitae actually sink in water.
- Air density is about 1.2 kg/m³, which sounds negligible — but the air in a single room (50m³) weighs about 60kg.
- API gravity is used in the crude oil trade, where a higher number indicates a lighter (more valuable) grade of oil, using an inverted scale based on water's density.
Frequently asked questions
Q. What is the difference between specific gravity and density?
Density has units (g/cm³); specific gravity is a unitless ratio to water. Because water's density is 1, the numbers coincide.
Q. How do I convert g/cm³ to kg/m³?
Multiply by 1,000. Steel at 7.85 g/cm³ is 7,850 kg/m³.
Q. Why does ice float on water?
Freezing arranges water molecules into a hexagonal structure that takes up more space, lowering density.