Enter water and reference conditions
Choose a mode first. Then use measured density or estimate water density from temperature, salinity, dissolved solids, and pressure.
Ready-to-use examples
Compare multiple water samples
Add measured or estimated samples, calculate their ratios, and export the complete comparison as a CSV file.
| Sample | Density (kg/m³) | Reference (kg/m³) | Specific gravity | Temperature | Status |
|---|---|---|---|---|---|
| No batch calculation has been run. | |||||
Temperature versus density chart
Visualize pure water or salinity-adjusted water across a selected temperature range. Values are engineering estimates.
The chart plots estimated density in kg/m³ against temperature in degrees Celsius.
Calculation history and saved presets
History remains in this browser only. It is not sent to a database by this calculator.
Recent calculations
Custom presets
Formula used
Specific gravity
SG = ρsample ÷ ρreferenceSpecific gravity is a ratio, so it has no unit. Both density values must represent compatible units before division.
Density from specific gravity
ρsample = SG × ρreferenceThis rearrangement calculates sample density when the ratio and reference density are already known.
Specific weight
γ = ρgSpecific weight measures weight force per unit volume. It depends on local gravitational acceleration.
Percentage difference
Δ% = ((ρsample − ρreference) ÷ ρreference) × 100The sign indicates whether the sample is denser or less dense than the chosen reference.
How to use this calculator
- Select the calculation mode that matches the known and unknown quantities.
- Choose a water type or enter a measured sample density.
- Set the sample temperature and temperature unit.
- Enter salinity or TDS when dissolved material should be included.
- Select the reference density, including its reference temperature.
- Enable the optional pressure correction only for approximate engineering work.
- Choose output units, decimal precision, and gravitational acceleration.
- Press the calculation button and review the ratio, density, specific weight, warnings, and calculation steps.
Approximate pure-water density reference table
These atmospheric-pressure values are generated from the same temperature equation used by the calculator.
| Temperature | Density kg/m³ | Density g/mL | SG relative to water at 4°C | Typical context |
|---|---|---|---|---|
| 0°C | 999.8676 | 0.999868 | 0.9998676 | Common laboratory range |
| 4°C | 1,000.0000 | 1.000000 | 1.0000000 | Near maximum density |
| 10°C | 999.7281 | 0.999728 | 0.9997281 | Common laboratory range |
| 15°C | 999.1285 | 0.999129 | 0.9991286 | Common laboratory range |
| 20°C | 998.2336 | 0.998234 | 0.9982336 | Common laboratory range |
| 25°C | 997.0751 | 0.997075 | 0.9970751 | Common laboratory range |
| 30°C | 995.6783 | 0.995678 | 0.9956783 | Heated water |
| 40°C | 992.2473 | 0.992247 | 0.9922473 | Heated water |
| 50°C | 988.0633 | 0.988063 | 0.9880633 | Heated water |
| 60°C | 983.2106 | 0.983211 | 0.9832106 | Heated water |
| 70°C | 977.7491 | 0.977749 | 0.9777491 | Heated water |
| 80°C | 971.7224 | 0.971722 | 0.9717224 | Heated water |
| 90°C | 965.1633 | 0.965163 | 0.9651633 | Heated water |
| 100°C | 958.0966 | 0.958097 | 0.9580966 | Heated water |
Understanding water specific gravity
What water specific gravity means
Specific gravity compares the density of a sample with the density of a selected reference. For liquids, the reference is usually water at a stated temperature. A value of 1 means the sample and reference have equal density. A value above 1 means the sample is denser than the reference, while a value below 1 means it is less dense. Because one density is divided by another density expressed in compatible units, the units cancel. The final specific-gravity value is therefore dimensionless.
It is tempting to say that water always has a specific gravity of exactly 1, but that statement omits the reference conditions. Water at 20°C compared with water at 4°C has a value slightly below 1 because water near 4°C is denser. Salty water can have a value above 1 because dissolved salts increase mass more than volume. A measured water sample may also contain suspended material, dissolved gases, or chemicals that alter its density.
Why temperature changes water density
Most liquids become less dense as they warm because their molecules occupy more volume. Water behaves unusually near freezing and reaches maximum density close to 4°C. From that point upward, density gradually decreases as temperature rises. This behavior matters in laboratories, process plants, reservoirs, aquariums, and pipeline calculations. A hydrometer reading taken at one temperature may need correction before comparison with a specification written at another temperature.
The calculator uses a practical polynomial estimate for pure liquid water near atmospheric pressure. It is suitable for general educational and engineering calculations, but specialized metrology work should use an applicable standard, calibrated instruments, and reference tables matched to the actual pressure and water composition.
How salinity and dissolved solids affect the result
Salinity is commonly expressed in practical salinity units or approximately parts per thousand. Ocean water near 35 PSU is noticeably denser than pure water at the same temperature. The seawater mode uses a recognized atmospheric-pressure polynomial over a practical oceanographic range. Brackish water falls between fresh water and seawater. Total dissolved solids are entered in milligrams per liter for a lighter fresh-water adjustment.
Composition matters. Two solutions with the same total dissolved solids can have slightly different densities because different ions and compounds change solution volume differently. The TDS adjustment in this calculator is intentionally approximate. Use measured density whenever a contractual, safety, billing, or laboratory decision depends on the result.
How pressure affects density
Liquid water is often treated as incompressible in basic calculations, but it compresses slightly under pressure. The optional pressure adjustment uses a constant compressibility approximation. It is useful for showing direction and approximate magnitude in ordinary conditions. It is not a substitute for a high-pressure equation of state. Very high pressure, elevated temperature, phase changes, dissolved gases, and unusual chemistry require more advanced property models.
Gauge pressure is measured relative to local atmosphere, while absolute pressure is measured relative to a vacuum. The calculator adds standard atmospheric pressure when gauge pressure is selected. Confirm the pressure convention before using values from a pump gauge, process transmitter, weather report, or technical datasheet.
Density, relative density, and specific weight
Density is mass per unit volume, such as kilograms per cubic meter. Relative density is another name commonly used for specific gravity. Specific weight is weight force per unit volume, such as newtons per cubic meter. Density does not depend on local gravity, but specific weight does. A tank of water has the same mass density on Earth and the Moon if its thermodynamic state is unchanged, yet its specific weight is much lower on the Moon.
This distinction is important in hydrostatics. Pressure increase with depth can be expressed using density and gravitational acceleration, or using specific weight directly. Pump head, buoyancy, tank loading, and open-channel calculations may use related quantities but should not treat them as interchangeable without checking units.
Common applications
Water specific gravity is used in hydraulics, plumbing, marine engineering, environmental monitoring, water treatment, food production, chemical processing, cooling systems, aquariums, laboratories, and quality control. It helps compare freshwater with seawater, interpret hydrometer readings, estimate buoyancy, convert between density and specific weight, assess dissolved material, and document sample conditions.
Pipeline and pump calculations may use density for mass flow and pressure-loss work. Marine users compare salinity-driven density changes because vessel buoyancy changes between fresh and salt water. Aquarium operators use specific gravity as a practical salinity indicator. Laboratory technicians record temperature because even a careful density measurement is incomplete without its thermal condition and reference basis.
Accuracy, uncertainty, and responsible use
No online calculator can know the actual composition or calibration history of a physical sample. Temperature probes, hydrometers, balances, volumetric glassware, pressure sensors, and salinity meters all introduce uncertainty. Bubbles, evaporation, contamination, suspended solids, meniscus reading, and insufficient temperature equilibration can also shift results.
Use the displayed precision as formatting, not as proof of accuracy. Six decimal places do not mean the source data are accurate to six decimal places. For regulated testing, custody transfer, medical use, safety-critical design, or contractual acceptance, follow the governing method and use calibrated equipment. This calculator is best treated as an educational tool, a planning aid, and a transparent way to check calculations.