Water Tank Capacity Calculator

The formula

Rectangular tank: volume = length × width × height. Upright cylinder: volume = π × (diameter ÷ 2)² × height. The calculator converts every length to meters first, so volumes are in cubic meters, then 1 m³ = 1,000 liters, 1 US gallon = 3.785411784 liters and 1 UK (imperial) gallon = 4.54609 liters.

With a water depth, the same formulas are used with the depth in place of the height. Because the sides are straight, the water volume is directly proportional to the depth.

Worked example

A rectangular tank 2 m long, 1.5 m wide and 1 m high holds 2 × 1.5 × 1 = 3 m³, which is 3,000 liters, or 792.5 US gallons, or 659.9 UK gallons. A cylindrical tank 1 m in diameter and 1.5 m high holds π × 0.5² × 1.5 = 1.178 m³, or 1,178.1 liters. Filled to a depth of 0.8 m, the rectangular tank holds 2 × 1.5 × 0.8 = 2.4 m³, or 2,400 liters, which is 80% of a full tank.

Measuring the tank

• Use inside measurements. The wall thickness of the tank reduces the space for water, and the outside size would overstate it.
• Measure the height to the level you will fill to. A tank is often not filled to the brim, so enter that level as the water depth.
• Mixed units are not supported. Choose one unit and measure everything in it.
• Changing the units box does not convert the numbers already typed in.

Limits

• It handles straight-sided rectangular tanks and upright cylinders only. Tapered, domed, conical-bottom, horizontal cylinder and irregular tanks are not covered.
• Fittings, pipes, internal baffles and ribs that take up space inside the tank are not subtracted.
• The result is the geometric capacity. A tank's labelled capacity may be a rounded figure, or a working capacity below the brim.
• Results update as you type, and the liters and gallons are shown to one decimal place.

More worked examples

A cylinder 1.2 m across and 1.5 m high holds 1.696 m³, which is 1,696.5 liters. Filled to 1 m it holds 1,131.0 liters, or 66.7% of a full tank.

A rectangular tank 6 ft × 4 ft × 4 ft is 2,718.4 liters, which is 718.1 US gallons or 598.0 UK gallons. In centimeters, 150 × 100 × 120 is 1,800.0 liters, and with the water at 90 cm there are 1,350.0 liters, or 75.0%.

A cylinder 5 ft across and 6 ft high holds 3,336.0 liters; at a water depth of 4.5 ft it holds 2,502.0 liters, also 75.0%. A cylinder 2 m across and 2 m high is 6,283.2 liters.

How the depth box behaves

• Leave it blank to get the full capacity, labeled "Capacity". If you fill it in, the full tank is labeled "Full tank" and the water at that depth is listed below it.
• A depth of 0 is accepted and gives 0.0 liters and 0.0% of a full tank.
• A depth above the tank height shows "The water depth cannot be more than the tank height." A negative depth shows "Please enter valid, positive values."
• The percentage is depth ÷ height, so it is the same for any straight-sided shape.

Rounding

Liters and gallons are shown to one decimal place and cubic meters to three. A 1 m cube therefore reads 1,000.0 liters, 264.2 US gallons, 220.0 UK gallons and 1.000 m³.