Reservoir Volume Calculator
Find how much water your hydroponic reservoir holds. Choose a rectangular or round tank, enter the inside size and the water depth, and get litres and US gallons.
How the calculation works
Volume is the footprint of the tank multiplied by the water depth:
Rectangular: volume = length × width × depth and Round: volume = π × (diameter ÷ 2)² × depth
Measurements are converted to centimetres, and 1,000 cm³ is 1 litre. Litres are then divided by 3.785 to get US gallons.
Example: a 60 × 40 cm tank with 30 cm of water holds 60 × 40 × 30 = 72,000 cm³ = 72 L, which is 72 ÷ 3.785 = 19.0 US gallons. A round tub 40 cm across with 30 cm of water holds π × 20² × 30 = 37,699 cm³, about 37.7 L or 9.96 US gallons.
With your volume known, use the hydroponic nutrient calculator to work out how much of each nutrient part to add.
Measure inside dimensions. Pumps, roots and media displace a little water, so treat the result as a close estimate.
Frequently asked questions
Should I measure the whole tank or only the water level?
Measure the water. Enter the depth the water actually reaches, not the height of the tank, because nutrient doses are based on the water volume. A tank that is filled to 25 cm in a 30 cm container holds less than the container's full capacity.
How do I measure an irregular tub?
Use the average inside length and width at the water line. Tubs that taper will hold less than a straight box of the same top size. For a precise figure, fill with a measured jug of water and count the litres.
Does the net pot, plants or media displace water?
Slightly. Roots, grow media and a pump take up some space, so your real volume is a little lower than the calculated one. For nutrient dosing the difference is usually small.
How many litres are in a US gallon?
One US gallon is 3.785 litres. A UK (imperial) gallon is 4.546 litres. This calculator uses the US gallon.