How to measure
Use these guides to identify the measurements the calculator needs. Drawings are not to scale.
C · Water depth: inside bottom to your intended waterline, not the tank rim. For a cylinder, use the inside diameter across the center and the same water depth.
Rocks, substrate, and equipment displace water. Enter a known displacement separately; zero gives the volume before displacement. For precise fill volume, measure the water you add.
Measure the water, not the label
Use internal dimensions and measure depth to the intended waterline. For a rectangular tank, inside length × inside width × water depth gives the space occupied by water before decorations. A cylinder uses π × radius² × water depth.
An inside footprint of 24 × 12 inches filled 12 inches deep holds 14.96 US gallons, or 56.63 liters, before displacement. A nominal tank label can differ because it may describe outside dimensions or a brim-full capacity.
Account for displacement
If you know how much water substrate, rocks, or equipment displace, enter it under Displaced water. Otherwise leave zero and treat the answer as an upper estimate at that waterline. Displacement must be smaller than the calculated volume.
One liter is 1,000 cubic centimeters. One US gallon is exactly 3.785411784 liters. These are US liquid gallons, not Imperial gallons. Changing units converts your entered dimensions and displacement; it does not just change their labels.
Filling with a container
Open Filling with a bucket or pitcher? beneath the result if you carry water by hand. Enter the amount you actually put in each container and choose US gallons, liters, US quarts, or milliliters. Changing the container unit converts its amount. This setting is separate from the tank’s units.
For the 14.96 US gallon example, a 5 US gallon bucket takes three trips: two full buckets and about 4.96 US gallons in the last one. A 2-liter pitcher takes 29 trips: 28 full pitchers and about 0.63 liter in the last one. Exact multiples have no extra trip. Use Copy fill plan to copy this breakdown.
This estimates filling an empty tank to the selected waterline, not topping up an already-filled tank. Stop at your intended waterline. If you use a hose or filling system, leave the section closed.
Limits
This supports rectangular tanks, straight cylinders, and bow fronts with a circular curve and equal straight side panels. It does not model corner tanks, tapered tanks, or irregular curves. The result is not a livestock stocking limit or a treatment dose. For precise actual water volume, measure the water added. No product database, live data, or personal information is used.
Measure a bow-front tank
Choose Bow front. Measure the inside length across the back, the back-to-front width at a straight side, the widest back-to-front width at the center, and the water depth. Use the inside bottom to your intended waterline for depth. Do not use the outside rim measurements or the tank’s advertised capacity.
The estimate adds a rectangular base to a circular segment, then multiplies that area by water depth. The extra bow is the center width minus the side width. A 100 cm long tank with 30 cm side width, 40 cm center width, and 40 cm water depth holds about 146.88 liters before displacement.
This assumes the front follows a circular arc across the full length and the sides are vertical. A different curve changes the result. For an exact fill amount, measure the water you add. The estimate is not a safe basis for medication dosing.