How dense is water? Pure liquid water peaks at about 1.000 g/cm3 (999.97 kg/m3, or 62.43 lb/ft3) near 4 degrees C (39.2 degrees F). However, at room temperature, 20 C (68 F), it is slightly lighter: 0.9982 g/mL, about 62.3 lb per cubic foot or 8.33 lb per US gallon.
How Dense Is Water in Other Units? Convert It
First, enter a density and pick its unit. The converter then shows the same value in metric and US units. For example, try 0.9982 g/cm3 for room-temperature tap water or 1.025 for seawater.
To begin with, density tells you how much mass fits into a given space. In other words, it is mass divided by volume. Water matters here because the metric system grew out of it. In fact, the original gram was the mass of one cubic centimeter of water, so water still sits at almost exactly 1 g/cm3 today.
That neat number hides a small twist, however. Specifically, water changes density with temperature, salt and pressure. For instance, cold water near 4 C is the densest, while warm water and ice are both lighter. As a result, lakes freeze from the top down, and ice cubes float in your drink.
The US Geological Survey explains this in its Water Science School page on water density, which lists values from freezing to boiling. Below you will find our own table, a comparison with ice and seawater, and finally a simple way to check density at home.
How Dense Is Water at Different Temperatures?
Above all, temperature is the biggest everyday factor. As water warms above 4 C, its molecules move faster and spread out, so the same mass takes up more room. Similarly, water cooled below 4 C starts forming open, ice-like clusters and expands a little. In addition, the values below come from the Kell equation for pure, air-free water at normal pressure, rounded to four significant figures.
| Temperature | g/cm3 (g/mL) | kg/m3 | lb/ft3 | lb/US gal |
|---|---|---|---|---|
| 0 C (32 F), liquid | 0.9998 | 999.8 | 62.42 | 8.344 |
| 4 C (39.2 F) | 0.99997 | 1,000.0 | 62.43 | 8.345 |
| 10 C (50 F) | 0.9997 | 999.7 | 62.41 | 8.343 |
| 15 C (59 F) | 0.9991 | 999.1 | 62.37 | 8.338 |
| 20 C (68 F) | 0.9982 | 998.2 | 62.32 | 8.330 |
| 25 C (77 F) | 0.9970 | 997.0 | 62.24 | 8.321 |
| 30 C (86 F) | 0.9956 | 995.6 | 62.16 | 8.309 |
| 37 C (98.6 F) | 0.9933 | 993.3 | 62.01 | 8.290 |
| 50 C (122 F) | 0.9880 | 988.0 | 61.68 | 8.246 |
| 60 C (140 F) | 0.9832 | 983.2 | 61.38 | 8.205 |
| 80 C (176 F) | 0.9718 | 971.8 | 60.67 | 8.110 |
| 100 C (212 F) | 0.9584 | 958.4 | 59.83 | 7.998 |
Overall, notice how small the change is from 0 to 30 C: less than half a percent. By contrast, boiling water is about 4 percent lighter than cold water. Print or save this chart if you work with hot liquids, because that 4 percent shows up in careful volume measurements.
Recommended Tools for Measuring Water Density
In fact, you only need three things to measure density: a way to find volume, a way to find mass, and a thermometer. First, a glass graduated cylinder gives far better volume readings than a kitchen jug. Next, a scale that reads to 0.1 g handles the mass. Finally, a hydrometer lets you read density (as specific gravity) directly from a floating glass stem.
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How Dense Is Water Compared With Ice, Seawater and Other Liquids?
Indeed, water is the reference that other liquids get compared against. So, if a liquid is denser than water, it sinks below it; if it is lighter, it floats on top. The table below therefore shows how common substances stack up.
| Substance | Typical density (g/cm3) | lb/ft3 | Floats or sinks in fresh water? |
|---|---|---|---|
| Fresh water, 20 C | 0.998 | 62.3 | – |
| Ice, 0 C | about 0.917 | about 57.2 | Floats |
| Seawater, surface | about 1.020 to 1.029 | about 63.7 to 64.2 | Sinks below fresh water |
| Vegetable oil | about 0.91 to 0.93 | about 57 to 58 | Floats |
| Honey | about 1.4 | about 87 | Sinks |
Ice, however, is the famous oddity. When water freezes, hydrogen bonds lock the molecules into an open hexagonal lattice. Consequently, ice takes up about 9 percent more space than the water it came from, so it is roughly 8 percent less dense. That is also why about a tenth of an iceberg shows above the waterline.
Seawater goes the other way, because dissolved salt adds mass without adding much volume. As a result, surface ocean water averages about 1.025 g/cm3. For more on the floating side of the chart, see how dense oil is compared with water. Meanwhile, our guide to how dense honey is covers the heavy end.
Density vs Specific Gravity vs Weight
These three terms get mixed up all the time, especially on product labels and in homebrewing. The table below therefore separates them.
| Term | What it means | Units | Value for water |
|---|---|---|---|
| Density | Mass per unit of volume | g/cm3, kg/m3, lb/ft3 | 0.9982 g/cm3 at 20 C |
| Specific gravity | Density of a liquid divided by the density of water | None (a ratio) | 1.000 by definition |
| Weight of a volume | How heavy a set amount is on a scale | lb per gallon, g per cup | 8.33 lb/gal; about 236 g per US cup |
Because specific gravity is a ratio, it has no units. For example, a liquid with a specific gravity of 1.4 is 1.4 times as dense as water. In addition, a gram per milliliter and a gram per cubic centimeter are the same thing, since 1 mL equals 1 cm3. If you want to turn a volume of water into a weight, our page on how much 3 liters of water is walks through it, and what mass is explains why mass and weight differ.
How to Measure How Dense Water Is at Home
Moreover, you can check the numbers above with basic kitchen or lab gear. Here, then, is the simplest method.
- Weigh the empty cylinder. Put a dry graduated cylinder on a scale that reads to 0.1 g, then press tare so it reads zero.
- Add a known volume of water. Pour in 100 mL and read the bottom of the curved surface (the meniscus) at eye level.
- Record the mass. Then write down the reading on the scale in grams.
- Check the temperature. Dip a thermometer into the water, because the result depends on it.
- Divide mass by volume. For instance, 99.8 g / 100 mL = 0.998 g/mL. Then enter that number in the converter above for other units.
- Compare with the table. Next, look up your temperature in the chart; a result within about 1 percent is good for kitchen gear.
Do and Don’t When Checking Water Density
Do
- Read the meniscus at eye level.
- Also note the water temperature every time.
- Tare the scale with the dry container on it.
- Let the water settle so bubbles rise out.
- Finally, repeat the test and average the results.
Don’t
- Use a plastic kitchen jug for precise volumes.
- Assume tap water equals pure water to four decimals.
- Mix up specific gravity and density units.
- Read a hydrometer while it touches the glass wall.
- Forget that salt makes water heavier.
How Dense Is Water Really? Honest Limits
The table describes pure, air-free water at sea-level pressure. Real water, however, differs slightly. For one thing, tap water carries dissolved minerals that raise its density by a tiny amount. Dissolved air, on the other hand, lowers it a little. Also, the classic “1 g/cm3” is a rounded figure; the true peak is about 0.99997 g/cm3 near 3.98 C. For cooking and most DIY work, rounding to 1 g per mL is fine. However, for lab work, calibration and fuel or chemical calculations, use the value at your actual temperature.
When Accuracy Really Matters
For most tasks, then, 1 kg per liter is close enough. Still, a few jobs need the exact figure:
- Calibrating glassware and pipettes. For example, labs weigh delivered water and divide by its density at the measured temperature to find the true volume.
- Brewing and winemaking. Hydrometers assume a reference temperature, so readings in warm wort need a correction.
- Engineering and tank sizing. For instance, a 1,000-gallon tank holds about 8,330 lb of water at room temperature, which matters for floor and stand loads.
- Swimming pools and aquariums. Similarly, saltwater tanks rely on specific gravity readings to keep fish healthy.
Frequently Asked Questions
How dense is water in g/mL?
Pure water is about 1.000 g/mL at 4 C and 0.9982 g/mL at 20 C (68 F). So for everyday use, 1 g per mL is close enough.
How dense is water in kg/m3?
It is about 1,000 kg/m3 at 4 C and, by contrast, 998.2 kg/m3 at room temperature, 20 C.
How dense is water in lb/ft3?
Water weighs about 62.43 lb per cubic foot at 4 C, whereas it weighs about 62.3 lb per cubic foot at 68 F.
At what temperature is water densest?
Water reaches its maximum density, about 0.99997 g/cm3, near 3.98 C (39.2 F). Above and below that point, however, it expands.
Why is ice less dense than water?
When water freezes, hydrogen bonds hold the molecules in an open hexagonal lattice. Ice therefore takes about 9 percent more space and has a density near 0.917 g/cm3, so it floats.
Is salt water denser than fresh water?
Yes. Dissolved salt adds mass, so surface seawater averages about 1.025 g/cm3 compared with about 0.998 g/cm3 for fresh water at room temperature.
How much does a gallon of water weigh?
A US gallon of water weighs about 8.33 lb (3.78 kg) at room temperature; by comparison, it weighs about 8.35 lb near 4 C.
Does hot water weigh less than cold water?
Per unit of volume, yes. Water at 100 C is about 0.958 g/mL, roughly 4 percent lighter than cold water. The mass of a fixed amount of water stays the same, though.
What is the specific gravity of water?
The specific gravity of water is 1.000 by definition, because it is the reference that other liquids get compared against.
Is 1 mL of water exactly 1 gram?
Almost. At 4 C, 1 mL of pure water has a mass of about 0.99997 g, and at 20 C about 0.9982 g. Rounding to 1 gram works for cooking.
How Dense Is Water? The Bottom Line
In short, water is about 1 g/cm3, or 62.4 lb per cubic foot, at its densest point near 4 C. At room temperature it drops a little, to 0.9982 g/mL and 8.33 lb per gallon. Meanwhile, ice is lighter, and seawater is heavier.
Finally, if you need the number in another unit, use the converter at the top of the page. For lab or engineering work, always look up the value at your real temperature instead of rounding to 1.
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