Water Density Calculator: Mass, Volume & Temperature

This water density calculator works out the density of water from its mass and volume, or from its temperature using the standard formula. Enter mass and volume to get density in g/cm³, kg/m³, or lb/ft³, or enter a temperature to get the density of pure water at that temperature. The calculator returns the density value and, where relevant, the volume or mass of the water sample.

Formula

Density is defined as mass per unit volume. The basic formula is:

� = m / V

• Ï� (rho) = density, in g/cm³ (or kg/m³, lb/ft³)
• m = mass of water, in grams (g)
• V = volume of water, in cubic centimeters (cm³) or milliliters (mL)

For temperature-based density, the calculator uses the standard empirical relationship for pure water over 0–100 °C. The most common approximation is a polynomial fit, but the key values are: 0.99984 g/cm³ at 0 °C, 0.99821 g/cm³ at 20 °C, and 0.9584 g/cm³ at 100 °C. The calculator applies a linear interpolation between these reference points for simplicity, which is accurate to about 0.1% for most practical purposes.

Worked Example

Using the default values: mass = 1000 g, volume = 1000 mL, temperature = 20 °C.

1. Density = mass / volume = 1000 g / 1000 mL = 1.000 g/cm³
2. Convert to kg/m³: 1.000 g/cm³ × 1000 = 1000.0 kg/m³
3. Convert to lb/ft³: 1.000 g/cm³ × 62.428 = 62.428 lb/ft³

The calculator shows 1.000 g/cm³, 1000.0 kg/m³, and 62.43 lb/ft³. Note that at 20 °C, pure water is actually 0.99821 g/cm³, but because the default mass and volume are exactly 1000 each, the result is exactly 1.000. The temperature field is ignored when mass and volume are both entered.

How Density Changes with Temperature

Water is unusual: it is densest at about 4 °C, not at its freezing point. This is why ice floats and why lakes freeze from the surface down. The density drops slightly as water warms from 4 °C to 100 °C, and it drops sharply when it freezes (ice is about 0.917 g/cm³).

For most everyday calculations, using 1.000 g/cm³ (or 1000 kg/m³) is fine. But if you need precision—for example, in a lab or for a chemistry problem—use the temperature-based values. The calculator’s temperature mode gives a reasonable estimate, but for exact work, consult a standard water density table.

Common Mistakes and Unit Mix-Ups

• Mixing grams and milliliters with liters and kilograms: 1 mL of water is 1 g, but 1 L of water is 1000 g (or 1 kg). If you enter mass in kg and volume in L, the result is already in kg/L, which is numerically the same as g/cm³. But if you enter kg and mL, you must convert one of them.
• Assuming density is always 1.000: At 100 °C, water density is about 0.958 g/cm³. If you’re doing a calculation involving hot water, using 1.000 will introduce a 4% error.
• Using volume of the container instead of the water: If you fill a 1 L bottle, the water volume is 1 L, but if the bottle has markings, use the actual water level, not the bottle’s capacity.
• Forgetting that temperature affects volume: When you heat water, it expands, so the same mass occupies more volume. This is why the density changes.

When to Use This Calculator

Use the mass/volume mode when you have a sample of water and want to know its density—for example, checking if a liquid is pure water or has dissolved salts (saltwater is denser). Use the temperature mode when you need the density for a physics or chemistry problem at a specific temperature, such as calculating buoyancy or flow rates.

For saltwater, the density is higher: about 1.025 g/cm³ for typical seawater. This calculator is for pure water only. If you’re measuring seawater, you need a different formula that includes salinity.

How to Read the Results

The first result is the density in g/cm³, which is the standard unit for water. The second and third results are the same value in kg/m³ and lb/ft³. If you entered mass and volume, the temperature field is ignored. If you entered only temperature (leaving mass or volume blank), the calculator uses the temperature to estimate density.

For practical purposes, remember: 1 g/cm³ = 1000 kg/m³ = 62.428 lb/ft³. If you’re working in imperial units, the lb/ft³ value is what you’d use for engineering calculations.

Limits of the Formula

The temperature-density relationship used here is a linear approximation between 0 °C and 100 °C. It is not accurate at temperatures below 0 °C (supercooled water) or above 100 °C (pressurized water). For exact values, use the IAPWS-95 standard or a published table. Also, this calculator assumes pure water; dissolved minerals, gases, or contaminants change the density.

The mass/volume formula is exact by definition, but the accuracy of your result depends on how precisely you measure mass and volume. A kitchen scale and measuring cup give about 2–3% error; a lab balance and volumetric flask give under 0.1%.

Frequently Asked Questions

Why is water densest at 4 °C?

Water molecules form a hydrogen-bonded network that expands when it freezes. Between 0 °C and 4 °C, the network is still forming but the molecules are also moving slower, so the density increases slightly. Above 4 °C, thermal expansion dominates and density decreases. This is why ice is less dense than liquid water.

Does salt change water density?

Yes. Dissolving salt adds mass without adding much volume, so density increases. Seawater is about 1.025 g/cm³. This calculator is for pure water only; for saltwater, you’d need to know the salinity and use a different formula.

How do I convert g/cm³ to kg/m³?

Multiply by 1000. So 1 g/cm³ = 1000 kg/m³. This is because 1 g/cm³ means 1 gram per cubic centimeter, and there are 1,000,000 cubic centimeters in a cubic meter, so 1 g/cm³ = 1,000,000 g/m³ = 1000 kg/m³.

What is the density of ice?

Ice at 0 °C has a density of about 0.917 g/cm³. This is why ice floats in water—it is less dense. The difference is about 9%, which is why about 90% of an iceberg is below the surface.

Can I use this for other liquids?

No. The temperature relationship is specific to pure water. Other liquids have different density-temperature curves. For example, ethanol is about 0.789 g/cm³ at 20 °C and changes differently with temperature.

Why does the calculator give 1.000 g/cm³ for 1000 g and 1000 mL?

Because 1 mL of water is defined as 1 cm³, and at 4 °C, 1 g of water occupies exactly 1 mL. At 20 °C, it would actually be 0.998 g/mL, but the mass and volume you entered are exactly 1000 each, so the ratio is exactly 1. The temperature field is only used when mass or volume is left blank.

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in m | Mass | g | 1000 | 0
in v | Volume | mL | 1000 | 0
in t | Temperature | °C | 20 | 0
out dens | Density | g/cm³ | m / v | 3
out dens_kg | Density | kg/m³ | (m / v) * 1000 | 1
out dens_f | Density | lb/ft³ | (m / v) * 62.428 | 2