Specific Gravity Calculator

Specific gravity (also called relative density) is the ratio of the density of a substance to the density of a reference substance, almost always pure water at 4 °C. Because it is a ratio of two densities, specific gravity is a dimensionless number — it has no units. A value of exactly 1.000 means the substance has the same density as water; values above 1 mean the material is denser than water, and values below 1 mean it is lighter.

The specific gravity calculator on this page turns a simple mass and volume measurement into a complete density profile. It computes the substance density, the specific gravity relative to your chosen water reference, a temperature-corrected value, the petroleum-industry API gravity, and both Baumé scale readings. It also tells you whether the substance will float, sink, or stay neutrally buoyant in water. This makes it useful far beyond a textbook exercise: clinical labs read urine specific gravity, brewers track fermentation, and biochemists confirm the concentration of glycerol, sucrose, and salt solutions.

In biology and medicine, specific gravity is one of the fastest ways to estimate solute concentration without expensive instruments. Whole blood sits near 1.06, normal urine ranges from about 1.005 to 1.030, and seawater is roughly 1.025. Because dissolved proteins, salts, and sugars all raise density, a single specific gravity reading reflects the total dissolved load of a fluid.

The calculator first finds the density of your sample from its mass and volume, then divides that density by the reference water density you supply. The two-step relationship is shown below, and it is exactly the math the tool runs internally.

When you already know a substance's density, switch to From Density mode and the calculator skips straight to the ratio while also reporting the equivalent mass for 100 mL and the equivalent volume for 100 g. Density itself is mass divided by volume, so the core formula chains those two ideas together: measure, divide, compare to water.

• Density is grams per milliliter (g/mL), numerically equal to grams per cubic centimeter.
• Specific gravity is that density divided by the reference water density, leaving a pure number.
• Using a reference of exactly 1.000 g/mL makes the density and specific gravity values identical, which is why they often look the same on screen.

The specific gravity calculator offers two workflows. In From Mass/Volume mode you enter the measured mass in grams and the measured volume in milliliters, plus the temperature of the sample. In From Density mode you enter a known density directly, which is handy when reading a value from a reagent label or a reference table.

1. Pick a calculation mode using the two buttons at the top of the input card.
2. Weigh your sample and read its volume in a graduated cylinder, then type both numbers in.
3. Set the reference water density — leave it at 1.000 g/mL for standard work, or lower it slightly if your reference water is warm.
4. Enter the sample temperature so the tool can apply a small correction to the water reference.
5. Read the specific gravity, density, API gravity, Baumé readings, and buoyancy verdict in the results panel.

For the most reliable readings, measure mass on a calibrated balance to at least two decimal places and dispense volume with a volumetric pipette rather than a beaker. Small volume errors dominate the final result because volume sits in the denominator of the density calculation.

Water is densest near 4 °C and becomes slightly less dense as it warms. Because specific gravity is measured against water, the temperature of your reference matters. The calculator applies a linear approximation to estimate water density at the sample temperature and then recomputes a temperature-corrected specific gravity.

The correction the tool uses is shown in the table below. As temperature rises above 4 °C, the modeled water density falls, which slightly raises the corrected specific gravity compared with the raw value. For precise hydrometry — brewing, clinical urinalysis, or battery electrolyte testing — always note the temperature at which a reading was taken.

The model is water density = 1.0 − ((T − 4) × 0.0002), which is a useful first-order estimate over normal lab temperatures. For temperatures far above 40 °C, consult a full water-density table for tighter accuracy.

Two historical scales convert specific gravity into more convenient numbers for specific industries, and the calculator reports both. API gravity was developed by the American Petroleum Institute to grade crude oils: lighter oils float higher and earn higher API numbers, while heavier oils score lower. Baumé scales predate the metric density system and are still printed on hydrometers for acids, syrups, and brines.

The relationships the tool applies are:

• API gravity = (141.5 / SG) − 131.5
• Baumé (heavy liquids) = (145 / SG) − 145
• Baumé (light liquids) = (140 / SG) − 130

Notice that a substance denser than water produces a negative API gravity, because the formula was tuned for liquids lighter than water. For dense biological fluids such as blood or concentrated sugar syrups, the heavy-liquid Baumé scale is the more meaningful reading, while the light-liquid scale and API gravity are most informative for oils and alcohols that float.

Specific gravity quietly underpins many routine measurements in the life sciences. In clinical chemistry, urine specific gravity reflects the kidney's ability to concentrate or dilute urine; values that stay near 1.010 across samples can signal impaired concentrating ability, while high values point toward dehydration or heavy solute loads. In hematology, the density of blood and its components is used to separate plasma, buffy coat, and red cells during centrifugation and density-gradient work.

The reference values built into this calculator illustrate the spread of common biological fluids and reagents:

Density-gradient media such as sucrose and Percoll exploit these same principles to band cells and organelles by buoyant density, and brewers and winemakers track sugar conversion by watching specific gravity fall during fermentation.

The calculator translates each specific gravity result into a plain-language buoyancy verdict. The rule is simple and follows directly from Archimedes' principle: an object placed in water displaces its own volume of water, and whether it floats depends on how its density compares with that of water.

• SG < 1 — Floats: the substance is lighter than water and rises to the surface, like ethanol or oil.
• SG = 1 — Neutral: the substance is neutrally buoyant and remains suspended at any depth.
• SG > 1 — Sinks: the substance is denser than water and settles, like glycerol, honey, or dense brine.

This buoyancy logic explains everyday lab and field observations: why oil layers sit on top of an aqueous phase in a separating funnel, why a fresh egg sinks while a stale one floats as it loses density, and why dense salt solutions form a stable layer beneath fresh water. Reading the buoyancy status alongside the numeric specific gravity gives you an immediate, intuitive check on whether your measurement makes physical sense.