📖 How To Use

How to Use This Water Weight Calculator

Two modes, one result — pick whichever is easier for your situation:

Choose your input method If you already know the volume (e.g. from a tank label), choose "Enter Volume." If you have physical measurements, choose "Enter Dimensions" for a rectangular tank.
Enter the value(s) and select units For volume mode, type the amount and pick litres, gallons, cubic metres, etc. For dimension mode, enter Length, Width, and Height with their respective units — mix freely (e.g. length in feet, height in cm).
Select liquid type Fresh water is selected by default (1.000 kg/L). Choose salt water for marine tanks, or select a custom density for other liquids like diesel, oil, or milk.
Read your results Weight is shown in kg, lbs, metric tonnes, and Newtons — along with volume in litres and US gallons. Copy or print the results with one click.

Structural tip: The weight calculated here is the water alone. Add the tank's own weight (a plastic tank is usually only 2–4% of its water weight; steel and concrete tanks weigh much more) and any stand or frame. Our Water Tank Weight Calculator adds the shell for you. Use our Rooftop Load Bearing Calculator for complete structural analysis.

📐 The Formula

Water Weight Formula Explained

The weight of water follows a simple relationship between volume and density:

Weight (kg) = Volume (L) × Density (kg/L)
Fresh water:    Weight (kg) = Volume (L) × 1.000
Salt water:     Weight (kg) = Volume (L) × 1.025
Weight (lbs) = Weight (kg) × 2.20462
Weight (N)    = Weight (kg) × 9.80665

For tanks measured in dimensions rather than volume, the calculator first computes volume in litres, then multiplies by the liquid density.

Water Weight per Cubic Foot and Cubic Metre

Engineers and contractors working in imperial units often need weight per unit volume rather than per litre. At standard temperature, fresh water weighs:

1 cubic foot (ft³) of water = 62.4 lbs (28.3 kg)
1 cubic metre (m³) of water = 1,000 kg (2,204.6 lbs)
1 cubic yard (yd³) of water = 1,685.6 lbs (764.6 kg)

To convert a volume in cubic feet to weight, multiply by 62.4 lbs/ft³. This figure is standard in structural and plumbing engineering for calculating hydrostatic load, pipe fill weight, and excavation dewatering volumes.

Water Density at Different Temperatures

Pure water is densest at about 4 °C (39 °F), 1.000 kg/L. It becomes slightly lighter as temperature rises — relevant for hot water tanks and industrial applications. Values below follow the standard (IAPWS-based) density tables; USGS publishes matching figures.

Temperature	Density (kg/L)	Weight of 1,000 L	Difference vs 4°C
4°C (39°F)	1.00000	1,000.0 kg	—
10°C (50°F)	0.99970	999.7 kg	−0.30 kg
20°C (68°F)	0.99821	998.2 kg	−1.79 kg
40°C (104°F)	0.99222	992.2 kg	−7.78 kg
60°C (140°F)	0.98320	983.2 kg	−16.80 kg
100°C (212°F)	0.95840	958.4 kg	−41.60 kg

For most household and commercial purposes, the difference is negligible, and using 1.000 kg/L errs slightly on the heavy, safe side. For hot-water systems the bigger issue is expansion: water heated from 4 °C to 60 °C takes up about 1.7% more space, which is why heating systems need expansion vessels.

Common Liquid Densities

Liquid	Density (kg/L)	Weight of 1,000 L
Fresh water (4°C)	1.000	1,000 kg
Seawater (typical)	1.025	1,025 kg
Drinking water (20°C)	0.998	998 kg
Milk (whole)	1.030	1,030 kg
Cooking oil	0.920	920 kg
Diesel fuel	0.850	850 kg
Petrol / Gasoline	0.740	740 kg
Concrete slurry	2.400	2,400 kg

How Much Do Common Water Containers Weigh?

Quick reference for standard container and tank sizes, calculated at 1 kg/L (fresh water, 4°C):

Container	Volume	Weight (water only)
1 gallon jug	3.79 L	8.34 lbs (3.79 kg)
5 gallon jug	18.9 L	41.7 lbs (18.9 kg)
55 gallon drum	208 L	459 lbs (208 kg)
275 gallon IBC tote	1,041 L	2,294 lbs (1,041 kg)
330 gallon IBC tote	1,249 L	2,753 lbs (1,249 kg)
1,000 L tank	1,000 L	2,205 lbs (1,000 kg)

These figures are for water weight only — add the container's own empty (tare) weight for total handling or shipping weight.

🏗️ When to Use This

Common Use Cases for Water Weight Calculation

🏠

Rooftop Tank Installation

Find the full weight of water plus tank before choosing a spot. Roofs are designed for far less than a full tank puts on its footprint — about 20 psf (98 kg/m²) for ordinary US roofs — so get an engineer to place it.

🚛

Transportation & Logistics

Calculate payload weight for tanker trucks, shipping containers, and rail cars to stay within legal axle load limits.

🏊

Swimming Pools & Ponds

Every foot of water depth puts 62.4 psf on the floor below (every metre, about 1,000 kg/m²). Check decks, balconies and terraces before filling a hot tub or raised pond — US decks are typically designed for only 40 psf.

🌾

Agricultural Irrigation

Size pumps and supports for farm storage tanks accurately using total water weight rather than volume alone.

⚗️

Industrial Processes

Calculate reagent and coolant weights for chemical processing, food manufacturing, and HVAC systems where liquid density varies.

🚨

Emergency Preparedness

Plan how many water containers you can safely store on shelves or in a vehicle for disaster preparedness kits.

🧮 Worked Example

Worked example: a raised pond 8 ft × 4 ft × 2 ft deep

A homeowner plans a raised garden pond 8 ft long, 4 ft wide and 2 ft deep on a patio. In "Enter Dimensions" mode, with fresh water:

Volume: 8 × 4 × 2 = 64 ft³ = 1,812 L (479 US gallons).
Weight: 64 ft³ × 62.4 lb ≈ 3,995 lb (1,812 kg, 1.8 tonnes).
Pressure on the base: 2 ft × 62.4 = about 125 psf (610 kg/m²) — fine on a ground slab, but about three times the 40 psf a typical US deck is designed for, so never on a deck or balcony without an engineer.

❓ FAQ

Frequently Asked Questions

How much does 1 litre of water weigh?

1 litre of fresh water weighs almost exactly 1 kilogram (1 kg) at 4°C — the temperature at which water reaches its maximum density. At typical room temperature (20°C), it is marginally lighter at 0.998 kg. For all practical household and engineering calculations, 1 litre = 1 kg is accurate enough.

How much does 1,000 litres (1 m³) of water weigh?

Exactly 1,000 kg (1 metric tonne) at 4°C. In pounds, that is 2,204.6 lbs. A standard 1,000-litre IBC tote full of water weighs roughly 1,050–1,070 kg (about 2,320–2,360 lb) once you include the plastic bottle, steel cage and pallet, which weigh about 50–70 kg empty.

Does salt water weigh more than fresh water?

Yes. Seawater has an average density of about 1.025 kg/L, meaning 1,000 litres of seawater weighs 1,025 kg compared to 1,000 kg for fresh water. The extra weight comes from dissolved salts (mainly sodium chloride). Ocean salinity is typically about 33–37 grams of salt per litre depending on location, and temperature matters too, so real seawater ranges from roughly 1.020 to 1.030 kg/L.

How do I calculate water weight from a tank's dimensions?

For a rectangular tank: multiply Length × Width × Height (all in cm) to get cubic centimetres, divide by 1,000 to get litres, then multiply by the density (1 kg/L for fresh water) to get kilograms. This calculator does all of that automatically — just switch to "Enter Dimensions" mode and enter your measurements.

How much does a gallon of water weigh?

A US gallon of fresh water weighs approximately 8.34 lbs (3.785 kg). A UK/Imperial gallon is larger and weighs roughly 10.02 lbs (4.546 kg). Always clarify which gallon definition applies when working with US vs. international specifications.

How do I check if my roof can hold a water tank?

Calculate the total load: water weight + tank shell weight + frame weight. Divide the total load by the base area in square metres to get load per m². Compare it with the roof's design load — about 20 psf (98 kg/m²) for an ordinary US roof, or 1.5 kN/m² (about 150 kg/m²) for an accessible concrete roof under India's IS 875. A 1,000 L tank on a 1.0 m × 1.2 m base puts about 830 kg/m² (171 psf) of water alone on its footprint — many times more — so it needs a stand placed over beams, walls or columns and a structural engineer's sign-off. Use our Rooftop Load Bearing Calculator for a full assessment.

Why is this calculator useful for more than just water?

Any liquid stored in a tank has weight that impacts structural loads, pump sizing, and transportation planning. By selecting the correct density — whether for seawater, diesel, cooking oil, or a custom fluid — this calculator gives you accurate weight figures for any tank or container used in agriculture, industry, food production, or emergency storage.

✅ Sources & Review

Sources and review

Water weight is volume × density. The density values on this page come from these references:

USGS — Water Density: 1.000 g/cm³ at 4 °C, 0.998 at about 20 °C, 0.983 at 60 °C, 0.959 at 100 °C; 62.4 lb per cubic foot.
Engineering ToolBox — Water density and specific weight, reproducing IAPWS-based tables (e.g. 998.2 kg/m³ at 20 °C).
NOAA — Sea Water: salinity typically 33–37 g/L; 1,025 kg/m³ is the typical seawater density used in NOAA data products.
NIST SP 811 — unit conversions (1 US gallon = 3.785 L, 1 UK gallon = 4.546 L, 1 ft³ = 28.32 L, 1 lb = 0.4536 kg, standard gravity 9.80665 m/s²).

Reviewed by John Mac, PE, Water Systems Specialist

Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.

Last updated October 9, 2026

🔗 Related Tools