Corner Bow Front Aquarium Volume Calculator

1. Front Span: Measure the straight inside distance between the two front corners, where the curved glass begins, with the tape pulled straight across the top and not following the curve. If you know the length of one wall panel instead, the front span is that length multiplied by 1.414.
2. Bow Depth: Lay a straight edge across the two front corners and measure from it to the front glass at its centre, at a right angle to the edge. Alternatively, measure from the rear corner to the middle of the front glass and subtract half the front span.
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 true quarter circle (the distance from the rear corner to the middle of the front glass equals the length of a wall panel), use the Corner Cylinder calculator instead.
• If the front glass is a single flat diagonal panel, use the Corner calculator instead.
• If the tank has a flat back wall behind its curved front, with no rear corner, use the Bow Front calculator instead.

The calculator models two equal wall panels that meet at a 90-degree rear corner, with the front glass curved between their front ends. The base is the triangle between the walls, F² ÷ 4, plus a half-ellipse bow, π × F × B ÷ 4, so no wall length is needed. The half-ellipse is an approximation of the curve: for a front that is a circular arc with the same front span and bow depth, the result reads up to about 5% high, and for a true quarter circle the Corner Cylinder calculator is exact. A tank with short straight panels between the walls and the curve is not modeled, and its result will not match.

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 bow front aquarium with the following inside dimensions: 38-inch front span, 6-inch bow depth, 22 inches tall.

1. Triangle section: (38 × 38 ÷ 4) × 22 = 361 × 22 = 7,942 cubic inches
2. Bow section: π × (38÷2) × 6 × 22 ÷ 2 = π × 19 × 6 × 22 ÷ 2 = 3,939.56 cubic inches
3. Total volume: 7,942 + 3,939.56 = 11,881.56 cubic inches
4. Convert to gallons: 11,881.56 ÷ 231 = 51.44 US gallons
5. Convert to liters: 51.44 × 3.785 = 194.70 liters

Result: This corner bow front aquarium holds approximately 51.44 US gallons (194.70 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 front span along the curve:The front span is the straight inside distance between the two front corners, not the arc length along the glass. The arc is longer than the straight distance, so entering it overstates the front span and, with it, the whole base.
• Entering a wall panel's length as the front span:The front span is about 1.414 times the length of one wall panel, because the two wall panels meet at a right angle. Entering a wall panel's length as the front span makes the result far too small.
• Measuring bow depth from the rear corner:Bow depth is measured from the straight line across the two front corners, not from the rear corner. The distance from the rear corner to the middle of the front glass is half the front span plus the bow depth, so entering it as the bow depth makes the result far too large.