Quick answer
Mass = volume × water density, and density depends on temperature. One litre at 4 °C weighs 1 kg (999.97 kg/m³), which is 2.2046 lb.
Enter a volume, its unit and the water temperature. The calculator returns mass in kilograms and pounds, and the density used.
Related tools: Gold Weight Calculator: Mass of pure gold from its volume. Pipe Weight Calculator: Weight of a hollow round pipe from its outside diameter, wall thickness and length. Glass Weight Calculator: Weight of a glass pane from its dimensions.
How to use the Water Weight Calculator
- Enter volume (0 or more).
- Choose volume unit: Litres, Millilitres, Cubic metres, US gallons, US quarts and US cups and 3 more.
- Enter water temperature (°C) (between 0 and 40). It starts at 20.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Volume | A number | ≥ 0 |
| Volume unit | Choose one: Litres; Millilitres; Cubic metres; US gallons; US quarts; US cups; US fluid ounces; Cubic feet; … | Starts at Litres |
| Water temperature (°C) | A number | ≥ 0, ≤ 40, starts at 20 |
Formula and method
Formula
mass = volume × ρ(T); ρ(T) = 999.97495 × [1 − (T − 3.983035)² (T + 301.797) ÷ (522528.9 (T + 69.34881))] kg/m³
IEEE-754 double precision; shown to at most 6 decimal places.
Density comes from the Tanaka et al. (2001) equation for air-free water (VSMOW), valid from 0 to 40 °C and accurate to a few parts per million. Tap water, sea water and dissolved gases differ slightly. Volumes use exact US customary definitions.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Volume = 1; Volume unit = Litres; Water temperature (°C) = 4.
| Result | Value |
|---|---|
| Weight | 1 kg |
| Pounds | 2.2046 lb |
| Density | 999.97 kg/m³ |
Example 2
Inputs: Volume = 1; Volume unit = US gallons; Water temperature (°C) = 20.
| Result | Value |
|---|---|
| Weight | 3.7786 kg |
| Pounds | 8.3304 lb |
| Density | 998.21 kg/m³ |
Example 3
Inputs: Volume = 250; Volume unit = Millilitres; Water temperature (°C) = 25.
| Result | Value |
|---|---|
| Weight | 0.2493 kg |
| Pounds | 0.5495 lb |
| Density | 997.05 kg/m³ |
The first line is the headline result (weight). Below it the water Weight Calculator lists pounds and density, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Density changes with temperature
Water is densest at about 4 °C (999.97 kg/m³). At 20 °C it is 998.2 kg/m³, so a litre weighs 0.998 kg; at 80 °C it is about 971.8 kg/m³. For cooking the difference is negligible, but in a tank or pool it adds up: 10,000 L at 20 °C weighs about 18 kg less than at 4 °C.
Rules of thumb
One US gallon of water weighs about 8.34 lb and a litre about 1 kg. This tool uses a polynomial density formula for pure water; dissolved salts, as in seawater, make it heavier.
How the result changes with volume
Holding every other input at the first worked example, this table changes only volume. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Volume | Weight | Pounds | Density |
|---|---|---|---|
| 0.5 | 0.5 kg | 1.1023 lb | 999.97 kg/m³ |
| 1 | 1 kg | 2.2046 lb | 999.97 kg/m³ |
| 2 | 1.9999 kg | 4.4091 lb | 999.97 kg/m³ |
| 4 | 3.9999 kg | 8.8183 lb | 999.97 kg/m³ |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Volume: left empty shows "Enter volume." beside that field and no result.
- Water temperature (°C): entering "41" shows "Water temperature (°C) must be at most 40." beside that field and no result.
Choosing between the Water Weight Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Gold Weight Calculator](/construction/gold-weight/) | volume and unit | Mass |
| [Pipe Weight Calculator](/construction/pipe-weight/) | outside diameter, wall thickness and length | Pipe weight |
| [Glass Weight Calculator](/construction/glass-weight/) | length, width and thickness | Glass weight |
| [Metal Weight Calculator](/construction/metal-weight-calculator/) | material, shape and dimension A | Weight |
| [Rebar Weight Calculator](/construction/rebar-weight-calculator/) | bar size, length of each bar and number of bars | Total weight |
Assumptions and limitations
- Only 0 to 40 °C is supported
- Water above 40 °C or containing dissolved salt has a different density
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for volume and water temperature (°C) to confirm this.
Frequently asked questions
How much does a gallon of water weigh?
About 8.34 lb (3.78 kg) near room temperature.
Does salt water weigh more?
Yes, seawater is about 1.025 kg per litre.
Is this for ice?
No; ice is less dense, about 917 kg/m³.
What does the Water Weight Calculator calculate?
Weight of a volume of water at a given temperature. It returns Weight, Pounds and Density.
What formula does the Water Weight Calculator use?
mass = volume × ρ(T); ρ(T) = 999.97495 × [1 − (T − 3.983035)² (T + 301.797) ÷ (522528.9 (T + 69.34881))] kg/m³. Density comes from the Tanaka et al.
What do I need to enter in the water Weight Calculator?
You enter Volume, Volume unit and Water temperature (°C).
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Only 0 to 40 °C is supported.
What are the limits of this calculator?
Only 0 to 40 °C is supported. Water above 40 °C or containing dissolved salt has a different density.
What is an example of a water Weight result?
With volume 1, volume unit Litres and water temperature (°C) 4, the weight is 1 kg.
Where does the method come from?
The method follows: Tanaka, Girard, Davis, Peuto, Bignell, Metrologia 38 (2001) 301-309, Recommended table for the density of water between 0 °C and 40 °C; US gallon = 3.785411784 L exactly (NIST SP 811).
Can I rely on this calculator for a decision?
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health. For this calculator in particular: Only 0 to 40 °C is supported.
Related calculators
- Gold Weight Calculator — Mass of pure gold from its volume.
- Pipe Weight Calculator — Weight of a hollow round pipe from its outside diameter, wall thickness and length.
- Glass Weight Calculator — Weight of a glass pane from its dimensions.
- Metal Weight Calculator — Weight of a plate, round bar or square bar in common metals.
- Rebar Weight Calculator — Weight of reinforcing bar by size and length.
- Money Weight Calculator — Weight of an amount of US bills or coins.
Sources
- Tanaka, Girard, Davis, Peuto, Bignell, Metrologia 38 (2001) 301-309, Recommended table for the density of water between 0 °C and 40 °C
- US gallon = 3.785411784 L exactly (NIST SP 811)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.