Tank Volume Calculator

How it is calculated

• Rectangular: length × width × height.
• Upright cylinder: π × (diameter ÷ 2)² × height.
• Lying cylinder (like many plastic and steel tanks on roofs): the filled part is a segment of the circle, so 50% depth really is half full but 25% depth is only about 20% of the volume — the calculator works this out exactly.

1 cubic foot holds 28.3 litres, so a 6 × 4 × 4 ft underground tank holds 2,718 litres (about 598 imperial gallons). Many people in Pakistan buy tanks by gallons — note that tank makers often use imperial gallons (4.55 L), while US gallons are 3.79 L.

Weight on the roof

Water weighs 1 kg per litre, so a full 1,000-litre tank puts a tonne of weight on the roof, plus the tank itself. Make sure the slab or stand is designed for it. Use inside measurements; wall thickness of a concrete tank can easily reduce capacity by 10–15%. For aquariums, leave the top few centimetres empty and remember gravel and decorations take up space.