Find how dense a substance is compared with water. Start from a density, a mass and volume, or two weighings in air and water, and convert the result to °API, °Baumé, °Brix and °Plato.
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Use a density, a mass and volume, or two weighings.
Pick the water temperature your standard uses.
Convert to °API, °Baumé, °Brix and °Plato.
Specific gravity (SG), also called relative density, is the density of a substance divided by the density of a reference, usually water. It has no units: SG 2.7 means the material is 2.7 times as dense as water. Because water density changes with temperature, standards state the reference temperature, such as 60 °F in the oil industry or 20 °C in many labs.
The weighing method uses Archimedes' principle. An object submerged in water seems lighter by the weight of water it displaces, so SG = weight in air / (weight in air − weight in water). Jewellers use this to check gold and gemstones.
141.5 / SG − 131.5. Light crude oil is above 31.1 °API.
Sugar percentage of a solution, estimated from SG.
Float in a liquid and read SG directly from the stem.
Not quite. Density has units such as g/cm³, while specific gravity is a ratio without units. Relative to water at 4 °C, the numbers in g/cm³ and SG are almost identical.
Exactly 1 when compared with water at the same temperature.
Weigh the object in air, then weigh it hanging fully under water without touching the container. Divide the air weight by the difference.
Use the one your standard or recipe states. Oil uses 60 °F, many lab methods use 20 °C, and older textbooks use 4 °C.
They come from standard polynomial fits for sucrose solutions and wort and are good estimates, but they are not exact for other dissolved substances.
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