What Is the Density of Water in 25 Degrees Celsius?

Water has a density of roughly 997 kilograms per cubic meter (kg/m³) at 25 degrees Celsius, which is about 0.997 grams per milliliter (g/mL). This value is slightly less than the maximum density of 1,000 kg/m³ that water reaches at around 4°C. For most practical lab or engineering work at room temperature, the density of water at 25°C is taken as 0.997 g/mL.

Why Temperature Changes Water Density

Water molecules move faster as temperature rises, which pushes them slightly farther apart. This expansion means the same mass of water takes up more volume, so its density goes down. The effect is small but measurable. For example, at 20°C the density is about 0.998 g/mL, and at 25°C it drops to 0.997 g/mL — a difference of roughly 0.1% per degree National Institute of Standards and Technology. If you are calibrating a volumetric flask or running a precise chemical assay, that 0.001 g/mL shift can matter.

A quick example: 250 mL of water at 25°C has a mass of about 249.25 grams (250 mL × 0.997 g/mL). If you assumed the density was exactly 1.000 g/mL, you would overestimate the mass by 0.75 grams. That error is negligible for a cooking recipe but could throw off a titration or a density-gradient separation.

Key Takeaways

• At 25°C, the density of pure water is 0.997 g/mL (997 kg/m³), about 0.3% lower than its maximum density at 4°C.
• Density decreases as temperature rises because water expands, so always note the temperature when measuring or calculating water mass.
• For most everyday use (mixing drinks, filling a tank), the 0.997 value is close enough to 1.0 to ignore; for lab work or engineering, use the precise figure Engineering Toolbox.
• If you need density for a specific temperature or water type (saltwater, ultrapure), check a reference table rather than guessing.