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Water Density Calculator
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Calculate water density instantly by entering temperature and salinity. Get accurate results in kg/m³ or g/cm³.
Water reaches its maximum density (approximately 1 g/cm³) at around 4°C.
Enter a volume to automatically calculate the mass of water based on its current density.
The Kell equation is used to calculate pure water density variation with temperature at 1 standard atmosphere. Actual density can also be influenced by dissolved impurities, salinity, and pressure. Results are approximate estimations for pure water.
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Scenario 1: HVAC Water System Design — Designers need to determine the density of circulating water. By entering the temperature difference between supply and chilled water (e.g., 7-12°C) into our calculator, you can find the density change to calculate pump head and pipe pressure drop. An error of over 1% can lead to incorrect equipment sizing.
Scenario 2: Aquaculture Water Exchange Calculation — Shrimp farms exchange water daily. The density difference between freshwater and seawater (salinity 35 ppt) affects stratification and oxygen levels. Enter the pond water temperature and salinity into the calculator to see if the density matches the replacement water source, preventing stress on the shrimp postlarvae.
Scenario 3: Swimming Pool Chemical Mixing — When adjusting pH or adding chlorine, you need to know the pool water density to calculate chemical concentrations (ppm). Enter the water temperature (e.g., 28°C) and salinity (0~5 ppt) into the calculator to get the density instantly, saving you the trouble of looking up tables.
First, open our calculator. You will see two input fields: "Temperature (°C)" and "Salinity (ppt)". Let's walk through it using a set of real data:
How is it calculated? The underlying logic uses international standard formulas (based on IAPWS-95). It first looks up the pure water density table by temperature, then applies a salinity correction (adding about 0.8 kg/m³ per 1 ppt). The density of pure water at 25°C is approximately 997.0. With a 0 salinity correction, the result is 997.05.
Interpretation: The density of tap water at 25°C is around 997 kg/m³. If your measured value is significantly different (e.g., below 990 or above 1000), check your temperature sensor or see if the water is contaminated.
Comparison Example 1: At the same temperature of 25°C, change the salinity to 35 ppt (seawater). Enter 35, and the result becomes 1024.2 kg/m³. It is about 27 kg heavier than freshwater, meaning seawater density is 2.7% greater than freshwater. This is crucial for marine engineering—at the same 25°C, seawater provides more buoyancy.
Comparison Example 2: Extreme Low Temperature. Enter a temperature of 0°C and a salinity of 0 ppt. The result is 999.8 kg/m³. Note that it is not 1000—pure water reaches its maximum density at 4°C (1000.0), and the density is slightly lower at 0°C (ice-water mixture). Our calculator does not handle sub-freezing temperatures; please use caution for anything below 0°C.
| Temperature Range | Pure Water Density (kg/m³) | Meaning |
|---|---|---|
| 0–4°C | 999.8–1000.0 | Anomalous expansion zone; density increases as temperature rises. |
| 4–20°C | 1000.0–998.2 | Common domestic water temperatures; density slowly decreases. |
| 20–40°C | 998.2–992.2 | Hot water and bathing temperature range; note a density drop of about 0.6%. |
| 40–100°C | 992.2–958.3 | Hot water heating and industrial water; density drops significantly. |
For every 1 ppt increase in salinity, density increases by approximately 0.8 kg/m³; at 40 ppt salinity, density increases by about 32 kg/m³. If the calculated value is below the theoretical range, first verify your input units (the temperature field is in °C, not °F).
Q1: Why does my water temperature of 20°C show a pure water density of 998.2, while others tell me it's 1.0 g/cm³?
A: 1.0 g/cm³ ≈ 1000 kg/m³, which is the density of pure water at 4°C. At 20°C, the density is about 998.2 kg/m³, or roughly 0.9982 g/cm³. The difference is small but cannot be ignored in engineering calculations.
Q2: Can it calculate seawater? How is salinity measured?
A: Yes. Seawater salinity is typically measured using a hydrometer or conductivity meter, and the unit is ppt (grams of salt per kilogram of seawater). Normal seawater is about 35 ppt. Just enter this into the calculator.
Q3: How do I switch between kg/m³ and g/cm³ in the results?
A: Our calculator displays both units simultaneously on the right side, so there's no need to switch. The numerical relationship is: 1 g/cm³ = 1000 kg/m³.
Q4: Is the calculation accuracy guaranteed?
A: Within the range of 0–100°C temperature and 0–40 ppt salinity, the error compared to IAPWS-95 standard values is <0.05 kg/m³. Thermometer errors (e.g., ±0.5°C) will introduce an error of about ±0.2 kg/m³.
Q5: Why is the result not 1000 when I enter 0°C and 0 salinity?
A: Because the density of pure water at 0°C (freezing point) is approximately 999.8 kg/m³, which is not the maximum value. The maximum value occurs at 4°C (1000.0). We output based on scientific data.
Q6: Can it calculate high-pressure water in a hot water boiler?
A: No. This tool is only for standard atmospheric pressure. The density of water increases significantly under high pressure; please use steam tables or professional software.
Now you can try entering your own water temperature and salinity in the calculator above to see how much the density changes.
