Bowfront Aquarium Volume Calculator
Curved-front tanks hold a little more than their flat-sided footprint suggests. Enter the width, side depth, water height, and how far the front bows out, and this works out the true water volume in gallons and liters.
Bow depth is how far the front bulges out beyond the flat sides. If your spec lists a single center depth, subtract the side depth from it.
Rocks, substrate, and the gap below the rim displace water. Pick what matches your setup.
Formula & how it works
The footprint is split into two parts: the rectangle behind the bow, width × side depth, plus the curved bulge on the front. The bulge is approximated as a parabolic segment with area (2 ÷ 3) × width × bow depth.
Multiply the footprint by the water height for the box volume in cubic inches, then gallons = in³ ÷ 231 and liters = gallons × 3.785. The fill level then trims the geometric maximum down to a realistic filled volume.
Worked example
A 36 in wide bowfront with 12 in side depth, 20 in of water, and a 3 in bow gives a footprint of (36 × 12) + (2⁄3 × 36 × 3) = 432 + 72 = 504 in². Times 20 in of water that is 10,080 in³, or 43.6 US gallons full to the brim. At a typical −10% fill that is about 39 gallons, roughly 149 liters.
Getting the numbers right
Measure the water, not the glass
Use the height the water actually reaches, not the full glass height. Most tanks fill an inch or so below the rim, and that gap is real gallons you will not have. If you plan to run the tank lower for a specific reason, measure to that line.
Side depth versus bow depth
Side depth is the flat front-to-back measurement at the ends of the tank, where the sides are straight. Bow depth is only the extra distance the middle of the front pushes out past those sides. Manufacturers sometimes quote a single center depth for the deepest point — if so, subtract the side depth to get the bow this calculator wants.
Why the real volume is lower
Substrate, rock, driftwood, and equipment all take up space that water would otherwise fill, and heavily planted or reef aquascapes can displace a surprising amount. The fill level option lets you knock the geometric maximum down to something closer to what you will actually dose, heat, and change.