Specific Gravity Converter
Convert specific gravity between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Calculator
Adjust values & calculateCommon Specific Gravities
| Substance | SG |
|---|---|
| Gasoline | 0.72-0.78 |
| Ethanol | 0.789 |
| Olive Oil | 0.91 |
| Water (4C) | 1.000 |
| Seawater | 1.025 |
| Glycerin | 1.261 |
| Sulfuric Acid | 1.840 |
| Mercury | 13.546 |
Formula
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.
Last reviewed: December 2025
Worked Examples
Example 1: Petroleum API Gravity
Example 2: Brewing Sugar Content
Background & Theory
The Specific Gravity Converter applies the following established principles and formulas. Unit conversion is the process of expressing a quantity in a different unit of measurement while preserving its physical meaning. At the foundation of modern measurement lies the International System of Units (SI), which defines seven base units: the meter for length, kilogram for mass, second for time, ampere for electric current, kelvin for thermodynamic temperature, mole for amount of substance, and candela for luminous intensity. All other units, called derived units, are defined as algebraic combinations of these seven. Dimensional analysis is the principal method for performing unit conversions. By treating units as algebraic quantities that can be multiplied, divided, and cancelled, a conversion factor chain allows a value expressed in one unit to be rewritten in another without altering its physical magnitude. For example, to convert 60 miles per hour to meters per second, one multiplies by a chain of conversion factors each equal to one: (1609.34 m / 1 mile) × (1 hour / 3600 s). Metric prefixes enable compact expression of quantities across extreme ranges of magnitude. Standard prefixes span from nano (10^-9) through micro (10^-6) and milli (10^-3) up through kilo (10^3), mega (10^6), and giga (10^9), and beyond in both directions. These prefixes are strictly multiplicative and apply consistently to any SI base or derived unit. Temperature conversions require affine transformations rather than simple scaling. To convert Celsius to Fahrenheit the formula is °F = (°C × 9/5) + 32, while the conversion to the absolute Kelvin scale is K = °C + 273.15. These formulas reflect the different zero points and degree-size conventions of each scale. Significant figures govern how precision is preserved through calculations. A result should not express more precision than the least precise input value permits. In digital storage, IEEE and IEC standards distinguish between decimal prefixes (kilobyte = 1000 bytes) and binary prefixes (kibibyte = 1024 bytes), a distinction that has practical consequences for how storage capacity is reported by manufacturers versus operating systems. Unit coherence — ensuring that all quantities in an equation share a consistent unit system — is essential for obtaining correct results.
History
The history behind the Specific Gravity Converter traces back through the following developments. Human beings have been measuring and comparing quantities since before recorded history. The earliest known measurement units were body-based: the cubit (the distance from elbow to fingertip), the foot, the hand, and the digit. The furlong originated as the length of a furrow a team of oxen could plow without resting. These anthropomorphic standards were practical for local use but differed between regions and kingdoms, creating persistent difficulties in trade and construction. The ancient Egyptians standardized the royal cubit at approximately 52.4 centimeters and distributed calibrated granite rods to ensure consistency across building projects, including the pyramids. Roman engineers used the mile (mille passuum, one thousand double paces) and spread these standards throughout their empire via road networks. Despite these efforts, measurement diversity persisted across medieval Europe, hampering commerce. The French Revolution created political will for radical standardization. In 1795 France officially adopted the metric system, defining the meter as one ten-millionth of the distance from the equator to the North Pole along the Paris meridian. This gave the world its first fully decimal, rationally constructed measurement system. The Metre Convention of 1875 established the International Bureau of Weights and Measures (BIPM) in Sevres, France, creating a permanent international body to maintain physical artifact standards and coordinate global metrology. For over a century, the kilogram was defined by a platinum-iridium cylinder locked in a vault near Paris. In 1999, a stark demonstration of what unit inconsistency costs occurred when NASA's Mars Climate Orbiter was lost because one engineering team used pound-force seconds while another used newton seconds. The spacecraft entered the Martian atmosphere at the wrong angle and was destroyed, at a cost of 327 million dollars. In 2019 the SI underwent its most significant revision, redefining all seven base units in terms of fixed numerical values of fundamental physical constants such as the speed of light, Planck's constant, and the elementary charge. This eliminated any reliance on physical artifacts and made the measurement system permanently stable and universally reproducible.
Frequently Asked Questions
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.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy