Cylinder aquarium volume calculator

Cylinder volume formula

volume = π × (diameter ÷ 2)² × height. With inches, divide by 231 for US gallons; with centimeters, divide by 1,000 for liters.

Worked example

An 18-inch diameter, 36-inch tall column tank: radius 9 inches, π × 81 × 36 = 9,161 cubic inches ÷ 231 = 39.7 US gallons (150 liters). The water alone weighs about 330 lb, all of it on a footprint of only 1.77 square feet — around 190 lb/ft² before the stand — so tall cylinders need a very solid base.

Measuring a cylinder tank

• Measure the diameter across the widest point, through the center. If you can only reach around it, measure the circumference and divide by π (3.1416).
• Acrylic cylinders often have thick walls: enter the wall thickness under Glass, water level & substrate to get the inside volume.
• Half-cylinder tanks hold exactly half of the result for the full diameter.

Stocking a cylinder

Tall, narrow tanks have little surface area for gas exchange and little horizontal swimming space. Stock them more lightly than a rectangular tank of the same volume, add surface movement, and choose fish that use the full height, such as angelfish in larger columns, or a lightly stocked planted nano community in smaller ones.

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