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Density Converter

Converters · Added 15 August 2026

Convert density between metric and imperial units, from kilograms per cubic metre to pounds per gallon. Water sits at almost exactly 1 g/cm³, which makes it a useful reference point: anything denser sinks in water, anything less dense floats.

Result

1 g/cm³ in kilogram per cubic metre

1,000 kg/m³

1 g/cm³ = 1,000 kg/m³

The same value in every unit

Kilogram per cubic metre (kg/m³)
1,000
Gram per cubic centimetre (g/cm³)
1
Gram per millilitre (g/mL)
1
Kilogram per litre (kg/L)
1
Tonne per cubic metre (t/m³)
1
Gram per litre (g/L)
1,000
Milligram per litre (mg/L)
1,000,000
Pound per cubic foot (lb/ft³)
62.4279606
Pound per cubic inch (lb/in³)
0.036127292
Ounce per cubic inch (oz/in³)
0.578036672
Pound per gallon (US) (lb/gal (US))
8.34540445
Pound per gallon (imperial) (lb/gal (UK))
10.0224129
Slug per cubic foot (slug/ft³)
1.94032033

Fresh water is almost exactly 1 g/cm³ (1,000 kg/m³) at 4 °C, which is where the metric system's convenient round numbers come from. Density falls as things get hotter, so a precise figure needs a stated temperature.

How to use the density converter

  1. 1Enter the density value you have.
  2. 2Pick the unit it is in and the unit you want.
  3. 3Watch the gallon units — US and imperial gallons are different sizes.
  4. 4The table shows the same density in every unit at once.
  5. 5Swap the units to reverse the conversion.

Examples

Water

Input
1 g/cm³
Result
1,000 kg/m³ · 62.43 lb/ft³ · 8.345 lb/gal (US)

Water at 4 °C. It is slightly less dense at room temperature and much less as ice.

Structural steel

Input
7,850 kg/m³
Result
7.85 g/cm³ · 490.1 lb/ft³

Steel is about 7.85 times as dense as water.

Petrol

Input
0.745 g/cm³
Result
745 kg/m³ · 6.22 lb/gal (US)

Less dense than water, which is why spilled fuel floats.

About the density converter

Why density decides what floats

An object placed in a fluid displaces its own volume and experiences an upward force equal to the weight of that displaced fluid — Archimedes' principle. Whether it floats therefore comes down to a comparison of densities: less dense than the fluid and the buoyant force wins, denser and it sinks. Nothing about size or weight alone determines it.

This explains the apparent paradox of a steel ship. Steel is nearly eight times as dense as water, but a hull is mostly air, and the average density of the whole vessel — steel, air and cargo together — is well below that of water. A ship sinks when that average density rises above water's, which is what taking on water accomplishes.

It also explains why oil floats on water and why layered drinks work. Any set of liquids that do not mix will arrange themselves by density, densest at the bottom, given time and a still container.

The gallon problem, and other unit traps

The imperial units in this family carry all the ambiguity of their volume units. Pounds per gallon means two different things depending on which gallon: the imperial gallon is about 20% larger than the US one, so the same liquid gives noticeably different figures. Both are listed here separately, and any datasheet quoting lb/gal without saying which is incomplete.

The slug is the other unit that catches people out. It is the imperial unit of mass in the system where force is measured in pound-force — one slug is about 14.59 kilograms, the mass that accelerates at one foot per second squared under one pound-force. Slugs per cubic foot appears in American fluid dynamics work, and mistaking a slug for a pound produces an error of a factor of about 32.

The safest habit with density, as with most engineering quantities, is to convert everything to SI at the start, do the work, and convert back only for presentation. Density calculations frequently combine with volume and mass figures that may themselves be in mixed units, and each mixed-unit step is another opportunity for a factor to go astray unnoticed.

Frequently asked questions

What is specific gravity, and how does it relate to density?
Specific gravity, or relative density, is the ratio of a substance's density to that of a reference — water for liquids and solids, air for gases. Because it is a ratio it has no units. Since water is almost exactly 1 g/cm³, the specific gravity of a liquid is numerically very close to its density in g/cm³, which is why the two are often used interchangeably in practice. Strictly they are different: one is a measurement with units, the other a dimensionless comparison.
Why are g/cm³, g/mL and kg/L all the same number?
Because a millilitre is defined as exactly one cubic centimetre, and a litre as exactly one thousand of them. So a gram per cubic centimetre, a gram per millilitre and a kilogram per litre are three names for the identical quantity. All three are listed here because different fields habitually use different ones, and people search for the form their datasheet used.
Does temperature change density?
Yes, and for precise work the temperature must be stated. Most substances expand as they warm, so density falls. Water is a famous exception below 4 °C: it reaches maximum density at 4 °C and becomes less dense as it cools further, which is why ice floats and why lakes freeze from the top down rather than the bottom up. Published density figures always assume a reference temperature, commonly 4 °C or 20 °C.
How do I convert a volume to a weight?
Multiply the volume by the density, keeping the units consistent. Two litres of a liquid at 0.8 kg/L weighs 1.6 kg. This is the whole reason density matters in shipping and cooking: a litre of honey and a litre of oil occupy the same space and weigh substantially different amounts. For recipe ingredients specifically, the cooking converter has a density table for common ingredients built in.

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