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How To Convert Volume To Weight

By | Last update: 27 August 2019

A frequent question arriving in my email mailbox is "how can I convert a volume to a weight?" Most commonly, people are trying to find out how to convert from liters to metric tons - often for substances such as water, gas and oil. Questions also arrive from people who are trying to measure out cooking ingredients and need to convert from cups to grams or cups to tablespoons (these links take you to my converters - set up to assist you).

Converting a liter of liquid volume

The problem with this type of conversion is that it isn't as simple as it sounds. A metric ton is a unit of weight and liter is a unit of volume. Equally, the cup is a unit of volume and the gram a unit of weight. To complete a calculation such as this, you therefore have to factor in the density of the substance that you are trying to convert and include that in the formula calculation. The reason for this is obvious - a cup of feathers will weigh less than a cup of crude oil. So, the substance is important for an accurate conversion.

For those people looking for the formula for converting volume to weight, and vice-versa, it looks like this (adapted from answers.com):

Density = mass/volume (ρ=m/V). So V=m/ρ and has units (kilograms)/(kilograms per cubic meter)=cubic meter.

If you are dealing with other units, say pounds, as a unit of weight, 'then 1 kg corresponds to 2.21 lb at sea level in the sense that the weight of 1 kg is 2.21 lb at sea level. Similarly 1 lb corresponds to 453.6 g and 1 oz to 28.35 g' (Beiser, A. Physics, 5th ed, Addison Wesley, 1992)

Before you can go any further with your calculation, you need to find out the density of the substance that you are trying to convert. You should be aware that densities vary based upon temperature, where liquids are concerned.

To help you out with your conversion, I have developed a weight to volume converter. On the converter page, I have included a list of substances and density approximations for some common liquids, materials, metals and woods. There's also a cooking recipe converter for common cooking measurement conversions.

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