Corner Aquarium Volume Calculator

1. Leg 1 (wall side): Measure the inside length of one wall-side panel, from the inside corner where the two wall panels meet to the inside edge where the diagonal front glass begins.
2. Leg 2 (wall side): Measure the other wall-side panel the same way. The two legs do not need to be equal, and the diagonal front glass is not measured.
3. Height: Measure from the inside bottom of the tank up to the water line.

Measure inside dimensions, glass to glass, inside any frame or trim, and measure each dimension twice.

• If the front glass is a quarter-circle curve, use the Corner Cylinder calculator instead.
• If the front glass bows outward between the front ends of the two wall panels, use the Corner Bow Front calculator instead.

The calculator treats the front glass as a straight line between the ends of the two legs, so the base is a right triangle and the result is exact under that assumption. A tank with short straight panels between the walls and the front glass is not a right triangle, and the result will not match it.

This formula calculates the interior volume in cubic units matching your input measurements. If you measure in inches, the result is cubic inches; divide by 231 to convert to US gallons, or multiply gallons by 3.785 for liters. If you measure in centimeters, the result is cubic centimeters; divide by 1,000 for liters.

Consider a corner aquarium with the following inside dimensions: 24-inch leg 1, 24-inch leg 2, 20 inches tall.

1. Calculate triangle area: ½ × 24 × 24 = 288 square inches
2. Multiply by height: 288 × 20 = 5,760 cubic inches
3. Convert to gallons: 5,760 ÷ 231 = 24.94 US gallons
4. Convert to liters: 24.94 × 3.785 = 94.40 liters

Result: This corner aquarium holds approximately 24.94 US gallons (94.40 liters) of water when filled to the measured height.

Fill Height

The calculator above assumes you fill the tank to the full measured height. In practice, most aquarists keep the water level 1–2 inches below the rim to prevent overflow during water changes, when adding hands and equipment, or if fish splash. Use the fill height adjustment toggle in the calculator to enter your actual water line height for a more realistic volume estimate.

For tanks with open-top (rimless) designs, the gap between water surface and glass top is especially important to track. A 2-inch gap on a 20-inch tall tank reduces effective volume by 10%, which is significant for medication dosing.

Substrate Displacement

Gravel, sand, and planted substrates occupy space that would otherwise hold water. A 2-inch layer of gravel in a standard rectangular tank displaces roughly 5–8% of the total tank volume. Use the substrate displacement toggle in the calculator to subtract this volume from your water capacity estimate.

Rock and Decoration Displacement

Large rocks, driftwood, and dense decorations also displace water, which this calculator does not subtract. Use the aquarium displacement calculator to estimate how much.

For how glass thickness reduces interior volume on your specific tank size, see the glass thickness and volume loss guide.

The calculator displays estimated water weight for both freshwater (8.34 lbs per gallon) and saltwater (8.55 lbs per gallon at 1.025 specific gravity). These estimates help you determine whether your floor and stand can safely support the filled tank, substrate, and equipment combined.

Water weight estimates are approximate and based on standard conditions. Freshwater weight assumes pure water at 62 °F (16.7 °C) with a density of 8.34 lbs/gal (1.0 kg/L). Saltwater weight assumes a specific gravity of 1.025, typical of reef aquariums. Actual weight may vary depending on water temperature, salinity, dissolved minerals, and substrate displacement. Always verify that your aquarium stand and floor can support the total weight of the filled tank, substrate, equipment, and decorations before filling.

• Measuring outside dimensions: Glass or acrylic thickness ranges from 3 mm to 19 mm per panel. Using outside dimensions overstates volume, especially on smaller tanks where glass thickness is a larger proportion of total width.
• Mixing measurement units: Entering some dimensions in inches and others in centimeters produces nonsensical results. Use one unit system consistently and let the calculator handle conversions.
• Measuring the diagonal front panel instead of the two legs:The formula only needs the two wall-side legs (a and b), not the length of the diagonal front panel. Measuring the front glass and entering it as a leg will produce an incorrect volume — the front panel length isn't used in this calculation at all.
• Assuming both legs are equal:The two legs of a corner tank's triangular footprint don't have to match, especially on custom builds fitted to an irregular corner. Measure each wall-facing panel independently rather than assuming symmetry.