Specific Gravity Converter
Convert specific gravity between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
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\nAPI = (141.5 / 0.876) - 131.5\nAPI = 161.53 - 131.5 = 30.03\nDensity = 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\nDensity = 1.050 x 998.2 = 1048.11 kg/m3\nBaume (heavy) = 145 - (145/1.050) = 145 - 138.10 = 6.90\nApprox 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.
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