Specific Gravity Converter
Convert specific gravity between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Specific Gravity Converter
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Formula: Density = SG x Reference Density | API = (141.5 / SG) - 131.5
Worked example โ SG 0.876 = API 30.03 = 874.42 kg/m3 (light crude)
Formula
Density = SG x Reference Density | API = (141.5 / SG) - 131.5
Specific gravity is the ratio of a substance density to a reference density (typically water at a specified temperature). Multiplying SG by the reference density yields the absolute density. API gravity is an inverse petroleum scale where lighter oils have higher API values. The Baume scale provides another density classification used in food and chemical industries.
Worked Examples
Example 1: Petroleum API Gravity
Problem:A crude oil sample has a specific gravity of 0.876 at 60 degrees F. Calculate its API gravity and density.
Solution:API = (141.5 / SG) - 131.5 API = (141.5 / 0.876) - 131.5 API = 161.53 - 131.5 = 30.03 Density = 0.876 x 998.2 = 874.42 kg/m3
Result:SG 0.876 = API 30.03 = 874.42 kg/m3 (light crude)
Example 2: Brewing Sugar Content
Problem:A wort sample reads SG 1.050 before fermentation. What is its density and approximate sugar content?
Solution:Density = SG x reference density Density = 1.050 x 998.2 = 1048.11 kg/m3 Baume (heavy) = 145 - (145/1.050) = 145 - 138.10 = 6.90 Approx sugar: ~12.5 grams per 100 mL (from Baume scale)
Result:SG 1.050 = 1048.11 kg/m3, Baume 6.90
Frequently Asked Questions
What is specific gravity and how is it measured?
Specific gravity is the ratio of the density of a substance to the density of a reference substance, usually water at 4 degrees Celsius (998.2 kg/m3) or at 15.6 degrees Celsius (999.1 kg/m3). Since it is a ratio, specific gravity is dimensionless and has no units. It is measured using hydrometers, pycnometers, or digital density meters. A specific gravity greater than 1 means the substance is denser than water and will sink, while less than 1 means it will float.
What is the difference between specific gravity and density?
Density is an absolute measurement expressed in units like kg/m3 or g/cm3, while specific gravity is a relative (dimensionless) ratio comparing a substance's density to that of a reference material. To convert specific gravity to density, multiply by the reference density. For water-referenced specific gravity at standard conditions, the numerical value of SG is approximately equal to density in g/cm3. Specific gravity is preferred in many industries because it does not change with measurement units.
What is API gravity and how does it relate to specific gravity?
API gravity is a scale developed by the American Petroleum Institute to classify crude oils and petroleum products. The formula is: API = (141.5 / SG at 60 degrees F) - 131.5. Higher API gravity means lighter (less dense) crude oil. Light crude has API above 31.1, medium crude ranges from 22.3 to 31.1, and heavy crude is below 22.3. API gravity of 10 corresponds to the density of water. This inverse relationship means that as specific gravity increases, API gravity decreases.
Why does specific gravity change with temperature?
Most substances expand when heated, causing their density and specific gravity to decrease with rising temperature. This is why specific gravity measurements must specify the temperature, often written as SG 20/4 (substance at 20 degrees C referenced to water at 4 degrees C). In brewing, winemaking, and petroleum industries, temperature correction tables are used to convert measured specific gravity to standard conditions. Digital density meters automatically apply temperature corrections for high accuracy.
What are common applications of specific gravity?
Specific gravity is used extensively across many fields. In brewing and winemaking, it tracks fermentation progress by measuring sugar content. The petroleum industry uses API gravity for crude oil classification and pricing. Urinalysis uses urine specific gravity as a kidney function indicator, with normal range 1.005 to 1.030. Gemologists use it to identify minerals, and battery technicians check electrolyte specific gravity to assess charge levels in lead-acid batteries.
Why does the reference temperature appear as a notation like 60/60 F?
Specific gravity is a ratio of two densities, and both shift with temperature, so a value is meaningless without stating the conditions. The notation gives the sample temperature over the reference water temperature, so 60/60 F means both were measured at 60 degrees Fahrenheit, the petroleum industry convention. A 20/4 C figure compares a sample at 20 degrees Celsius with water at 4 degrees, where water reaches its maximum density of about 1000 kg per cubic metre.
How does a hydrometer actually read specific gravity?
A hydrometer floats at the depth where the weight of displaced liquid equals its own weight, which is Archimedes principle, so a denser liquid supports it higher and a lighter one lets it sink. The stem is graduated so the reading at the liquid surface gives the ratio directly. Accuracy depends on reading at the bottom of the meniscus, keeping the instrument free of the container walls, and applying a temperature correction unless the sample sits at the calibration temperature.
What is the difference between the Brix, Plato and Baume scales?
All three are density derived scales converted to a more useful quantity for a specific trade. Brix expresses sucrose content by mass percent and dominates juice and sugar work, Plato is the near identical brewing equivalent used for wort extract, and Baume is an older scale defined against salt solutions and still used in chemical and syrup processing. Each is ultimately read from the same underlying density or specific gravity measurement, so tables convert between them.
Why do lighter crude oils have higher API gravity numbers?
The API scale inverts specific gravity by definition, since API equals 141.5 divided by specific gravity minus 131.5. Substituting a specific gravity of 1 gives exactly 10 degrees API, so anything lighter than water reads above 10 and anything heavier reads below. Light crude around 35 to 40 API contains more short chain hydrocarbons and yields more high value distillate, which is why the number carries a price premium over a heavy sour grade.
What can specific gravity tell you about a solution concentration?
For a binary mixture such as sulfuric acid in water, antifreeze in coolant, or sugar in must, density rises or falls monotonically with the dissolved fraction, so a single specific gravity reading maps to a concentration through a published table. That is how battery state of charge and coolant freeze point are checked in the field. The method fails when a third component varies independently, because two different compositions can then share the same density.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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