Introduction / overview

Density Conversion turns a single density value into its equivalent in the units people actually meet — kilograms per cubic metre (the SI unit), grams per cubic centimetre, pounds per cubic foot, pounds per US gallon, and a full set of extras from tonnes per cubic metre down to milligrams per litre.

Type a value in any field and every other unit updates at once, in either direction — no formulas to juggle when a material datasheet says lb/ft³ but your project works in kg/m³.

It is the kind of tool you reach for when a construction spec lists pounds per cubic foot and you need kilograms per cubic metre, when a chemistry reference quotes grams per cubic centimetre and you want pounds per US gallon, or when you simply want to compare the density of two materials written in different unit systems. All fourteen units describe the same physical density, so nothing else has to be typed.

How to use / quick start

1Find the field whose unit matches the value you have — the “Metric units” section holds kilograms per cubic metre and per cubic decimetre, while “Imperial Units” holds pounds per cubic foot, per cubic yard, and per US gallon.
2Type the number. Every other field recalculates instantly to the same density.
3Read the unit you need. Each field has a selector on the right that switches it between all fourteen units, so you can show any result in the unit you want.

Example: a material spec of 1 lb/ft³ in kg/m³

Enter $1$ in the “Density in pounds per cubic feet” field. The converter converts through kilograms per cubic metre, then to the metric field:

1

\ \mathrm{lb/ft^3}

\times

16.0185

\ \mathrm{kg/m^3\ per\ lb/ft^3}

=

16.0185

\ \mathrm{kg/m^3}

The same entry also reads $0.0160185\ \mathrm{kg/dm^3}$ and $0.133681\ \mathrm{lb/US\ gal}$ , so you can see every equivalent in one pass.

Example: water at 1000 kg/m³ in imperial units

You can start from any unit. Enter $1000$ in the “Density in kilograms per cubic meters” field and read the imperial equivalents:

1000

\ \mathrm{kg/m^3}

\div

16.0185

\ \mathrm{kg/m^3\ per\ lb/ft^3}

\approx

62.428

\ \mathrm{lb/ft^3}

The same entry reads $62.428\ \mathrm{lb/ft^3}$ and $8.3454\ \mathrm{lb/US\ gal}$ — the two numbers people most often quote for water, and the source of a classic unit mix-up covered below.

Calculation method

Every field is converted through the kilogram per cubic metre, the SI derived unit of density: one kilogram of mass in one cubic metre of volume.

If $\rho_s$ is the value you entered and $f_s$ is the number of kilograms per cubic metre in one source unit, the shared density is:

\rho_{\mathrm{kg/m^3}} = \rho_s \times f_s

\rho_t

=

\rho_{\mathrm{kg/m^3}} \div f_t

=

\rho_s \times \frac{f_s}{f_t}

The conversion factors are exact definitions: $1\ \mathrm{lb} = 0.45359237\ \mathrm{kg}$ (the international pound), $1\ \mathrm{ft} = 0.3048\ \mathrm{m}$ , $1\ \mathrm{in} = 0.0254\ \mathrm{m}$ , and $1\ \mathrm{US\ gal} = 231\ \mathrm{in^3}$ , all listed in the NIST Guide to the SI conversion tables. Because every field stores kilograms per cubic metre, the same relationship works in reverse — you can enter any field and the rest follow.

How to read the method:

$\rho_{\mathrm{kg/m^3}}$ is the shared density expressed in kilograms per cubic metre.
$f_s$ and $f_t$ are the kilograms-per-cubic-metre factors for the source and target units, such as $1000\ \mathrm{kg/m^3\ per\ g/cm^3}$ or $16.0185\ \mathrm{kg/m^3\ per\ lb/ft^3}$ .
You can enter any editable field, so the conversion runs in both directions rather than only from kilograms per cubic metre outward.

Real-world examples

Structural steel in metric and imperial specs

Mild steel has a density of about $7850\ \mathrm{kg/m^3}$ . Enter it in the kilograms-per-cubic-metre field:

7850

\ \mathrm{kg/m^3}

=

7.85

\ \mathrm{kg/dm^3}

=

490.059

\ \mathrm{lb/ft^3}

=

65.5114

\ \mathrm{lb/US\ gal}

A European datasheet that quotes $7.85\ \mathrm{kg/dm^3}$ and a US handbook that quotes $490\ \mathrm{lb/ft^3}$ are describing the same steel — the converter makes the match obvious.

Air at sea level for engineering and aviation

Standard sea-level air has a density of about $1.225\ \mathrm{kg/m^3}$ . Enter it and read the imperial values:

1.225

\ \mathrm{kg/m^3}

=

0.001225

\ \mathrm{kg/dm^3}

=

0.0764743

\ \mathrm{lb/ft^3}

=

2.0648

\ \mathrm{lb/yd^3}

Air is roughly a thousand times less dense than water, which is why the same volume of air weighs so little — a fact that matters for ventilation, aerodynamics, and buoyancy calculations.

Water: the 62.4 lb/ft³ vs 8.34 lb/US gal mix-up

Water is about $1000\ \mathrm{kg/m^3}$ . Depending on the unit, that same density is written two very different ways:

1000

\ \mathrm{kg/m^3}

=

62.428

\ \mathrm{lb/ft^3}

=

8.3454

\ \mathrm{lb/US\ gal}

Both numbers describe the same water — a US gallon is only about $0.1337\ \mathrm{ft^3}$ , so a cubic foot of water weighs far more than a gallon of it. Confusing the two is one of the most common density unit errors.

Related concepts

One density, many names

A gram per cubic centimetre, a gram per millilitre, a kilogram per litre, a kilogram per cubic decimetre, and a thousand kilograms per cubic metre are all exactly the same density. Because a litre is a cubic decimetre and a millilitre is a cubic centimetre, the metric units collapse into one another:

1\ \mathrm{g/cm^3}

=

1\ \mathrm{g/mL}

=

1\ \mathrm{kg/L}

=

1\ \mathrm{kg/dm^3}

=

1000\ \mathrm{kg/m^3}

This is why the density of water is often written as $1\ \mathrm{g/cm^3}$ in chemistry and $1000\ \mathrm{kg/m^3}$ in engineering — the same value in different clothes.

Density vs. specific gravity

Specific gravity is a density divided by the density of water, so it is a pure number with no units. A material with a density of $7850\ \mathrm{kg/m^3}$ has a specific gravity of about $7.85$ — the same number as its density in grams per cubic centimetre. The converter works in absolute density, so you can read the value in any unit and divide by $1000\ \mathrm{kg/m^3}$ yourself if you need the specific gravity.

From density to the weight of a volume

Once you know a substance’s density, the natural next step is often “how much does this volume weigh?” — which is exactly what the density-based weight converters on this site do.

Gallons to Pounds Conversion

Convert a liquid volume to pounds (or back) using its density.

kg to Gallons Converter

Convert a mass in kilograms to US or UK gallons using an ingredient density.

Cubic Yards to Tons Calculator

Convert a bulk-material volume in cubic yards to metric tons using density.

Frequently asked questions

Why is water 62.4 lb/ft³ but only 8.34 lb/US gal?

Because a US gallon is a small volume — exactly $231\ \mathrm{in^3}$ , about $0.1337\ \mathrm{ft^3}$ . A cubic foot of water weighs about $62.4\ \mathrm{lb}$ , but a gallon of it weighs only about $8.34\ \mathrm{lb}$ . Both are the same density of roughly $1000\ \mathrm{kg/m^3}$ , just measured over different volumes.

Is 1 g/cm³ the same as 1000 kg/m³?

Yes, exactly. A gram is one thousandth of a kilogram and a cubic centimetre is one millionth of a cubic metre, so $1\ \mathrm{g/cm^3} = 10^{-3}\ \mathrm{kg} / 10^{-6}\ \mathrm{m^3} = 1000\ \mathrm{kg/m^3}$ . The converter shows this directly: enter $1$ in a field set to grams per cubic centimetre and the kilograms-per-cubic-metre field reads $1000$ .

What is the difference between lb/US gal and lb/Imperial gal?

The US liquid gallon is $231\ \mathrm{in^3}$ , while the Imperial (UK) gallon is about $277.42\ \mathrm{in^3}$ — roughly $20\%$ larger. A pound per US gallon is about $119.826\ \mathrm{kg/m^3}$ , whereas a pound per Imperial gallon is about $99.776\ \mathrm{kg/m^3}$ . This converter uses the US liquid gallon, so check which gallon a source is quoting before comparing values.

Density Conversion

Introduction / overview

How to use / quick start

Calculation method

Real-world examples

Frequently asked questions

Why is water 62.4 lb/ft³ but only 8.34 lb/US gal?

Is 1 g/cm³ the same as 1000 kg/m³?

What is the difference between lb/US gal and lb/Imperial gal?

Limitations

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