What Is the Water Tank Capacity Calculator?
This tool estimates how much water a storage tank can hold, expressed in liters, cubic meters and US gallons. It supports the two most common tank shapes: rectangular (box-shaped) tanks and cylindrical (round) tanks. Simply enter the internal dimensions in meters and the calculator returns the full capacity. It's useful for sizing rainwater harvesting systems, agricultural and livestock water storage, swimming pool top-ups, septic and process tanks, and household water reserves.
How to Use It
First choose the tank shape. For a rectangular tank, enter the Length, Width and Height. For a cylindrical tank, enter the Diameter and Height (depth). Always use the internal measurements of the tank so you get the true holding capacity rather than the outer footprint. The result is shown in liters, with cubic meters and US gallons for convenience.
The Formula Explained
One cubic meter of water equals exactly 1,000 liters, so every volume is converted by multiplying by 1,000.
For a rectangular tank: $$V = L \times W \times H \times 1000$$ For a cylindrical tank the cross-section is a circle, so: $$V = \pi \times r^{2} \times h \times 1000$$ where the radius \(r\) is half the diameter. US gallons are obtained by multiplying liters by \(0.264172\).
Worked Example
Suppose you have a rectangular tank 2 m long, 1 m wide and 1 m high. The volume is \(2 \times 1 \times 1 = 2\) m³, which equals $$2 \times 1000 = 2{,}000 \text{ liters}$$ (about 528 US gallons). For a cylindrical tank 1.5 m in diameter and 1 m high, the radius is 0.75 m, so $$V = \pi \times 0.75^{2} \times 1 = 1.767 \text{ m}^3 \approx 1{,}767 \text{ liters}$$
FAQ
Do I measure inside or outside the tank? Use internal dimensions for an accurate capacity. Wall thickness reduces the volume slightly.
What if my tank is only partly full? Replace the height with the actual water depth to find the current stored volume.
Can I use other units? This calculator expects meters. Convert other units to meters first (e.g. 150 cm = 1.5 m).
