In short: fresh water is about 998.2 kg/m³ (0.998 g/cm³) at room temperature, and reaches its maximum of about 999.97 kg/m³ near 4 °C. Seawater is denser — typically around 1,025 kg/m³ at 20 °C — because dissolved salt adds mass with little added volume. Use the calculator above for any temperature and salinity.
These figures are planning aids based on published density data. For structural, regulatory or safety-critical work, confirm with a licensed engineer.
How to calculate the density of water
Density is mass packed into a given volume. For pure water, density depends almost entirely on temperature; for natural or process water, dissolved salts add a further, fairly predictable, increase. This calculator works in two steps:
This calculator converts your temperature to the Kell equation's fresh-water density, then adds the salinity term if you specify one. For everyday questions — “is water denser than seawater?” or “how much does density change near boiling?” — the fresh-water figure alone usually answers it. For oceanographic, aquarium or brine work, the salinity field matters.
Worked example. Take fresh water at 25 °C. The Kell equation gives a density of 997.04 kg/m³ (0.99704 g/cm³). Add a typical seawater salinity of 36 g/kg: 36 × 0.757 ≈ 27.3 kg/m³, giving a seawater density of about 1,024.3 kg/m³ — a specific gravity of roughly 1.024 relative to fresh water at its densest.
Density vs. specific gravity, in one line. Density is mass per volume (kg/m³, g/cm³…); specific gravity (SG) is a ratio — this calculator compares density to fresh water at its maximum, about 999.972 kg/m³ near 4 °C — so fresh water at room temperature reads slightly under 1.000, and seawater reads a little over 1.02.
Why temperature changes water's density
Heat water and it expands — the same mass spreads into a larger volume, so density drops. Water is unusual: it reaches its maximum density at about 4 °C (39 °F), not at freezing. Hydrogen bonds pull cooling water molecules into a more open lattice as it nears 0 °C, which is also why ice floats. Above 4 °C, water behaves more like other liquids and simply becomes less dense as it warms, dropping about 4% by the time it reaches 100 °C.
This calculator uses the Kell equation, the standard polynomial fit for the density of air-free water between 0 °C and 150 °C at one atmosphere, accurate to a few parts per million. For the full density curve across that entire range, see our density-by-temperature calculator. Full method detail is on our methodology page.
Density of fresh water by temperature
The values this calculator uses for fresh water (0 g/kg salinity), from freezing to boiling. Every cell matches the live tool above.
| Temperature | kg/m³ | g/cm³ | lb/ft³ | lb/US gal | Specific gravity |
|---|---|---|---|---|---|
| 0 °C / 32 °F | 999.84 | 0.9998 | 62.42 | 8.344 | 0.9999 |
| 4 °C / 39 °F (densest) | 999.97 | 1.0000 | 62.43 | 8.345 | 1.0000 |
| 10 °C / 50 °F | 999.70 | 0.9997 | 62.41 | 8.343 | 0.9997 |
| 20 °C / 68 °F (room) | 998.20 | 0.9982 | 62.32 | 8.330 | 0.9982 |
| 25 °C / 77 °F | 997.04 | 0.9970 | 62.24 | 8.321 | 0.9971 |
| 37 °C / 99 °F (body) | 993.33 | 0.9933 | 62.01 | 8.290 | 0.9934 |
| 60 °C / 140 °F | 983.20 | 0.9832 | 61.38 | 8.205 | 0.9832 |
| 80 °C / 176 °F | 971.80 | 0.9718 | 60.67 | 8.110 | 0.9718 |
| 100 °C / 212 °F (boiling) | 958.36 | 0.9584 | 59.83 | 7.998 | 0.9584 |
Quick reference: typical salinity and density
Common water types at 20 °C (68 °F). Handy when you just need a ballpark without opening the calculator.
| Water type | Typical salinity | Density (kg/m³) | Specific gravity |
|---|---|---|---|
| Fresh / tap / distilled | ~0 g/kg | 998.2 | 0.9982 |
| Brackish (estuary) | ~0.5–15 g/kg | 998.6–1,009.5 | 0.9986–1.0097 |
| Seawater (ocean average) | ~35 g/kg | 1,024.7 | 1.0247 |
| Red Sea / hypersaline | ~40 g/kg | 1,028.5 | 1.0285 |
Worked examples
Cold tap water in winter
999.7 kg/m³
Fresh water at 10 °C is slightly denser than room-temperature tap water, since it's closer to water's 4 °C density peak.
Ocean water sample
1,024.3 kg/m³
A 25 °C seawater sample at 36 g/kg salinity — typical of open ocean — has a specific gravity of about 1.024 relative to fresh water.
Hot tub at 37 °C
993.3 kg/m³
Body-temperature fresh water is about 0.5% less dense than room-temperature water — noticeable to instruments, not to swimmers.
What else affects the density of water
Dissolved salts. Salinity is the biggest everyday factor beyond temperature. Ocean water at ~35 g/kg is about 2.7% denser than fresh water; the calculator's salinity field models this linearly, which holds well up to about 40 g/kg but understates true seawater physics at brine-level salinities.
Pressure. Water is nearly incompressible, so pressure has a negligible effect at household or building scale. It becomes measurable at ocean depth — see our water pressure at depth calculator for how pressure builds with depth.
Dissolved air and impurities. Tap water carries tiny amounts of dissolved gas and minerals. The effect on density is well under a tenth of a percent — invisible for practical purposes, which is why this calculator models pure, air-free water as the fresh-water baseline.
Frequently asked questions
What is the density of water?
Fresh water is about 998.2 kg/m³ (0.9982 g/cm³) at room temperature, 20 °C. It is densest at about 999.97 kg/m³ near 4 °C, and becomes less dense as it warms toward boiling or cools toward freezing.
Does water density change with temperature?
Yes. Fresh water reaches its maximum density near 4 °C. Warming it toward 100 °C drops the density to about 958.4 kg/m³, roughly a 4% decrease. Cooling below 4 °C also lowers density slightly, which is why ice floats.
Why is water densest at 4°C?
Hydrogen bonds between water molecules pull them into a more open, cage-like arrangement as the liquid approaches freezing, which is why ice is less dense than liquid water. That same effect slightly reduces density just above freezing, so the true density peak sits near 4 °C (39 °F) rather than at 0 °C.
What is the density of seawater?
Typical ocean water, with a salinity of about 35 grams of dissolved salt per kilogram, has a density of roughly 1,025 kg/m³ at 20 °C — about 2.7% denser than fresh water at the same temperature, because the dissolved salts add mass without adding much volume.
How accurate is this calculator?
Fresh-water density comes from the Kell equation, the reference standard for water density between 0 °C and 150 °C, accurate to a few parts per million. The salinity adjustment is a linear approximation calibrated to typical seawater (about +26.5 kg/m³ at 35 g/kg) and is best suited to everyday and estuarine salinities, not hypersaline brine. Full detail is on our methodology page.
Sources & references
- Kell, G. S. (1975). Density, thermal expansivity, and compressibility of liquid water from 0° to 150 °C. Journal of Chemical & Engineering Data, 20(1), 97–105.
- National Institute of Standards and Technology (NIST). Thermophysical Properties of Fluid Systems.
- International Bureau of Weights and Measures (BIPM). The International System of Units (SI).
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)