Water Density Calculator
Calculate water density at any temperature from 0°C to 100°C with optional salinity correction. Get density results in kg/m³, g/ml, and lb/ft³ instantly.
About This Calculator
The Water Density Calculator computes the density of pure and salt water at any temperature between 0°C and 100°C using the validated 5th-order polynomial formula for water density as a function of temperature. It also applies a salinity correction based on the Millero equation for seawater density calculations.
Water density is not constant — it varies significantly with temperature and salinity. Pure water reaches its maximum density of 999.97 kg/m³ at approximately 4°C, then decreases as temperature rises. This calculator helps engineers, scientists, students, and marine professionals quickly determine water density for fluid mechanics, oceanography, aquaculture, and desalination applications.
The calculator provides density in three common units: kilograms per cubic meter (kg/m³), grams per milliliter (g/ml), and pounds per cubic foot (lb/ft³). It also shows which common objects (eggs, fruit, wood types, plastic) will float or sink at the given water conditions.
Formula
For pure water at 1 atm: ρ(T) = 999.83311 + 0.0752·T − 0.0089·T² + 7.36413×10⁻⁵·T³ − 4.74639×10⁻⁷·T⁴ + 1.34888×10⁻⁹·T⁵, where T is temperature in °C. Salinity correction: Δρ = 0.8245·S where S is salinity in ‰. Reference: Millero et al. (1980), Deep Sea Research.
Regional Notes
India: Used for drinking water treatment plant design (BIS standards), reservoir thermal stratification studies, and marine engineering along the 7,500 km coastline. Standard seawater density is typically 1025 kg/m³ at 25°C for Indian Ocean conditions.
United States: The US Geological Survey (USGS) uses water density for streamflow measurements. EPA water quality monitoring requires density-corrected conductivity readings. Seawater density at 35‰ and 20°C is 1024.9 kg/m³.
United Kingdom: The UK Environment Agency uses water density for river flow gauging and flood modeling. The Cefas (Centre for Environment, Fisheries and Aquaculture Science) uses seawater density for fisheries research in UK waters.
Frequently Asked Questions
What is the density of water at 4°C?
Water reaches its maximum density of 999.97 kg/m³ (approximately 1000 kg/m³) at 4°C. This is why ice floats — water below 4°C expands and becomes less dense, so ice at 0°C (917 kg/m³) is less dense than liquid water.
How does temperature affect water density?
Water density decreases as temperature increases above 4°C due to thermal expansion. At 20°C, density is about 998.2 kg/m³. At 50°C, it drops to 988.0 kg/m³. At 100°C (boiling), density is approximately 958.4 kg/m³. The calculator uses a 5th-order polynomial validated against standard reference tables.
How does salinity affect water density?
Adding salt increases water density. Seawater at 35‰ salinity has a density of about 1024.9 kg/m³ at 20°C compared to 998.2 kg/m³ for pure water. The Dead Sea, with salinity of 342‰, has a density of about 1240 kg/m³, making it easy to float. Each 1‰ increase in salinity raises density by approximately 0.82 kg/m³.
How is water density calculated?
Water density is calculated using a 5th-order polynomial: ρ(T) = 999.83311 + 0.0752·T - 0.0089·T² + 7.36413×10⁻⁵·T³ - 4.74639×10⁻⁷·T⁴ + 1.34888×10⁻⁹·T⁵, where T is in °C. Salinity correction adds 0.8245·S kg/m³ where S is salinity in ‰. This formula provides accurate results between 0°C and 100°C.
Does an egg float or sink in water?
A fresh egg (density ~1035 kg/m³) sinks in pure water (1000 kg/m³) but can float in salt water if the salinity is high enough. The calculator shows which common objects float or sink at your selected temperature and salinity. Eggs typically float in water with salinity above 60‰.
How do I convert water density between units?
The calculator provides density in three common units: kg/m³ (SI standard), g/ml (equivalent to g/cm³, divide kg/m³ by 1000), and lb/ft³ (multiply kg/m³ by 0.062428). For example, 1000 kg/m³ = 1.0000 g/ml = 62.43 lb/ft³.
Why is water most dense at 4°C?
Water has a unique property called density anomaly. As water cools from room temperature, hydrogen bonding causes molecules to pack more efficiently, increasing density until 4°C. Below 4°C, water begins to form ice-like crystal structures that are less dense, causing the density to decrease. This anomaly allows aquatic life to survive winter as ice floats on top.