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Specific Gravity Calculator

Specific Gravity (SG) = Density of Substance ÷ Density of Water

Example: Steel has a density of 7850 kg/m³, giving it a specific gravity of 7.85 relative to water (1000 kg/m³).

Calculate the relative density of materials compared to pure water. Supports metric density inputs. Essential for geology, brewing, chemical engineering, and material science.

Material Parameters

Calculated Ratio

Specific Gravity (SG) 7.850
Result Context: An SG greater than 1.000 means the substance sinks in water. An SG less than 1.000 means it floats.

Common Materials Specific Gravity Chart

Material Nominal Density Specific Gravity (SG)
Pure Water (at 4°C) 1000 kg/m³ 1.000
Gold (Pure) 19300 kg/m³ 19.30
Iron / Steel 7850 kg/m³ 7.85
Concrete 2400 kg/m³ 2.40
Oak Wood (Dry) 750 kg/m³ 0.75
Ethanol (Alcohol) 789 kg/m³ 0.789
Air (at sea level) 1.225 kg/m³ 0.001

Understanding Specific Gravity

Specific gravity is a dimensionless ratio comparing a material's density to a reference (usually water at 4°C = 1000 kg/m³). Because it's a ratio, it has no units — it's simply a number that tells you how much heavier or lighter a substance is compared to water.

SG > 1.0: Material sinks in water (denser)
SG = 1.0: Material has same density as water
SG < 1.0: Material floats on water (lighter)
Reference: Water at 4°C = 1000 kg/m³ = 1.000 SG

Applications Across Industries

Brewing: SG measures sugar content — Original Gravity (OG) and Final Gravity (FG) determine alcohol by volume. Geology: Identifies minerals by comparing measured SG to known values (quartz = 2.65, calcite = 2.71).

Medicine: Urine specific gravity (1.005-1.030) assesses kidney function and hydration. Construction: Concrete aggregate SG affects mix design — lightweight aggregates (SG 0.5-1.0) produce insulating concrete; normal weight aggregates (SG 2.4-2.9) provide structural strength.

Frequently Asked Questions — Specific Gravity

What is specific gravity?
Specific gravity (SG) is the ratio of a substance's density to the density of a reference material, typically pure water at 4°C (1000 kg/m³). It is a dimensionless number. SG > 1.0 means the substance sinks in water; SG < 1.0 means it floats.
How do you calculate specific gravity?
Specific Gravity = Density of Substance ÷ Density of Water (reference). Formula: SG = ρ_substance / ρ_water. Example: Gold has density 19,300 kg/m³, so SG = 19,300 / 1000 = 19.30.
What is the specific gravity of water?
Pure water at 4°C has a specific gravity of exactly 1.000 by definition, since it is the reference material. Water at 20°C has SG ≈ 0.998 due to thermal expansion. Seawater has SG ≈ 1.025 because dissolved salts increase its density.
What does specific gravity tell us about a material?
Specific gravity indicates buoyancy, density classification, and material purity. In brewing, it measures sugar content during fermentation. In geology, it helps identify minerals. In medicine, it's used for urine and blood tests. In construction, it indicates concrete aggregate quality.
How is specific gravity used in brewing?
Specific gravity measures dissolved sugars in wort before fermentation (Original Gravity, OG) and after (Final Gravity, FG). ABV = (OG − FG) × 131.25. Typical beer OG ranges from 1.030 to 1.080. The hydrometer measures SG to track fermentation progress.

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