How to convert from volume to mass (incorrectly called weight)?

To convert from volume to mass, we just need the definition of density formula:

mass = density × volume

Example 1

How much do 2 cubic meters of gasoline weigh in kilograms if the gasoline density is 750 kg/m³?

Plugging the values in the formula, we get

mass = density × volume = 750 × 2 = 1500 Kg

This is a simple calculation, which directly applies the density formula, works fine when the density value we have is based on the same unit of volume and mass we are using. For example, mass in kg and volume in liters. If we have, for example, mass in pounds and volume in gallons, but the density unit is in kg/m³ (for example) we should do something to adjust our density formula. That is: we must transform gallons to cubic meters as well as pounds to kilograms.

To transform the mass from pounds to kilograms we should multiply the mass in pounds by 0.45359237. We will call 0.45359237 the mass conversion factor - mcf

Mathematically we can write:

mass in kilograms = mass in pounds × mcf or

mkg = mlb × mcf (1)

To transform the volume from gallons to cubic meters we should multiply the volume in cubic meters by 0.003785411784. We will call 0.003785411784 the volume conversion factor - vcf

Mathematically we write:

volume in cubic meters = volume in gallons × vcf or

v = vgal × vcf (2)

Now, dividing the equation (1) by the equation (2), we get

mkgv = mlb × mcfvgal × vcf, or

mkgv = mlbvgal × mcfvcf, but mkgv is, by definition, the density (d) in kg/m³, so

d = mlbvgal × mcfvcf

Rearranging the equation above we get:

mlb = d × vgal × vcfmcf

Finally, we can generalize this formula for any units of mass and volume, since we know how to find the values for mcf and vcf (Check the conversion factor tables below).

m = d × v × vcfmcf (3)

That is exactly the formula that we use in our mass ⇌ volume calculator.

Now let's apply this formula to solve the next question.

Example 2

How much does 2 cubic feet of concrete weigh in tonnes if the concrete density is 2350 kg/m³?

m = d × v × vcfmcf (3)

m = 2350 × 2 × 0.0283168465921000 =

m = 2350 × 2 × 0,000028317 =

m = 0,133057 tonne

Conversion factors chart - vcf and mcf

These tables contain the most frequently used vcf and mcf.

Volume UnitFactor to convert to m³ (vcf)
UK fluid ounce0.0000284130625
US fluid ounce0.00002957352956
UK gallon0.00454609
US gallon0.003785411784
Mass UnitFactor to convert to kg (mcf)

Densities for some substances / Materials (Examples)

acetone784.58 kg/m³25 °C
alcohol, ethyl785.06 kg/m³25 °C
alcohol, methyl786.51 kg/m³25 °C
benzene873.81 kg/m³25 °C
kerosene817.15 kg/m³60 °F
methane464.54 kg/m³-164 °C
milk970 kg/m³15 °C
oil engine885 kg/m³25 °C

Get more densities


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