Aquarium Volume by Brand

Aquarium manufacturers print nominal gallon ratings and exterior dimensions on their packaging. This reference table shows those published exterior dimensions, the nominal label volume, and the geometric volume calculated from exterior measurements — so you can see at a glance why your tank’s actual water volume differs from its label, and use the correct figure for dosing, filtration sizing, and water changes.

⚠️ All dimensions in this table are exterior measurements as published by manufacturers or major retailers. Interior (water-holding) dimensions are smaller due to glass thickness — typically ¼″ per panel on tanks up to 29 gallons and ½″ per panel on larger tanks. Calculated volume uses exterior dimensions and will slightly overstate true water capacity. For precise dosing, always measure inside the glass. See our measurement guide for step-by-step instructions.

Brand Model / Size Exterior L × W × H (in) Nominal Label (gal) Calculated Vol. (gal) Calculated Vol. (L)
Aqueon Standard Glass Rectangle
Aqueon 2.5 Mini 12.19 × 6.13 × 8.13 2.5 2.63 10.0
Aqueon 5.5 16.19 × 8.38 × 10.5 5.5 6.17 23.4
Aqueon 10 Leader 20.25 × 10.5 × 12.56 10 11.56 43.8
Aqueon 15 24.25 × 12.5 × 12.75 15 16.73 63.3
Aqueon 20 High 24.25 × 12.5 × 16.75 20 21.98 83.2
Aqueon 20 Long 30.25 × 12.5 × 12.75 20 20.87 79.0
Aqueon 29 30.25 × 12.5 × 18.75 29 30.69 116.2
Aqueon 30 Breeder 36.19 × 18.25 × 12.94 30 37.00 140.1
Aqueon 40 Breeder 36.19 × 18.25 × 16.94 40 48.43 183.3
Aqueon 55 48.25 × 12.75 × 21 55 55.93 211.7
Aqueon 75 48.5 × 18.5 × 21.13 75 82.07 310.7
Aqueon 90 48.5 × 18.5 × 25.38 90 98.58 373.2
Aqueon 125 72.5 × 18.5 × 23.38 125 135.75 513.9
Aqueon 150 72.5 × 18.5 × 29.5 150 171.29 648.4
Fluval
Fluval Flex 9 14 × 13 × 13 9 10.24 38.8
Fluval Flex 15 16 × 15 × 15 15 15.58 59.0
Fluval Spec III 2.6 10 × 8 × 11.5 2.6 3.98 15.1
Fluval Spec V 5 17.2 × 11.2 × 9.8 5 8.17 30.9
Fluval Spec 16 21.5 × 11.5 × 17 16 18.20 68.9
Fluval Flex models have a curved (bow-front) design. The rectangular calculation shown overestimates actual volume. Use the Bow Front calculator for accuracy.
Marineland
Marineland 2.5 12 × 6 × 8 2.5 2.49 9.4
Marineland 5 16 × 8 × 10 5 5.54 21.0
Marineland 10 20 × 10 × 12 10 10.39 39.3
Marineland 20 High 24 × 12 × 16 20 19.95 75.5
Marineland 20 Long 30 × 12 × 12 20 18.70 70.8
Marineland 29 30 × 12 × 18 29 28.05 106.2
Marineland 55 48 × 13 × 20 55 54.03 204.5
Marineland 75 48 × 18 × 21 75 78.55 297.3
Marineland 110 48 × 18 × 30 110 112.21 424.8
Coralife BioCube
Coralife BioCube 16 15 × 16.75 × 17.5 16 19.03 72.0
Coralife BioCube 32 20.25 × 21.875 × 21.5 32 41.23 156.1
BioCube models include a built-in rear filtration chamber that reduces display water volume by approximately 20–30% below the full tank exterior calculation.

Why Calculated Volume Differs from Nominal Label Volume

Nominal volume is a marketing label based on a rounded figure, often using approximate exterior or even older interior measurements from when the tank design was first standardised decades ago. Calculated volume using the formula L × W × H ÷ 231 applied to exterior dimensions produces a slightly different number — sometimes higher, sometimes lower than nominal — because exterior dimensions include the glass panels themselves. A 10-gallon Marineland tank (20 × 10 × 12 in exterior) calculates to 10.39 geometric gallons, while the 29-gallon (30 × 12 × 18 in) calculates to only 28.05 — demonstrating that “nominal” is not a consistent ratio to exterior dimensions. For more detail on standard tank measurements, see aquarium volume by size. For the complete breakdown of how each shape formula works, see aquarium volume formulas. For a detailed breakdown of nano tank sizes under 10 gallons across multiple formats, see the nano aquarium volume guide.

For practical purposes — dosing medications, calculating filter turnover, planning water changes — use the nominal label volume as a baseline and measure your actual fill level with the displacement calculator to arrive at the true water volume in your specific tank. For standard rectangular tanks, the rectangular calculator gives a precise result from inside dimensions. If your tank has a curved front panel, the bow-front calculator accounts for the extra volume in the bow section.

If you cannot measure your tank at all, see how to calculate aquarium volume without dimensions for four practical alternatives.

Brand Volume Questions

Are the dimensions on the box exterior or interior?
Always exterior. Manufacturers measure the outside of the glass panels. Interior dimensions are smaller by the glass thickness on each side — typically ¼ inch per panel on tanks up to 29 gallons, and ½ inch per panel on 55-gallon and larger tanks. For a 48-inch-long 55-gallon tank with ½-inch glass, the interior length is approximately 47 inches.
Why does my 55-gallon tank not actually hold 55 gallons?
The nominal label is a rounded marketing figure. The exterior geometric volume for a common 55-gallon Aqueon tank (48.25 × 12.75 × 21 in) calculates to about 55.68 gallons — but that uses exterior dimensions. Interior volume after accounting for glass thickness is closer to 52–53 gallons brimful. With substrate and a 1–2 inch air gap, usable water is typically 48–50 gallons.
Do Aqueon and Marineland tanks share the same dimensions?
Many standard sizes do share near-identical exterior dimensions. Aqueon (formerly All-Glass Aquarium) and Marineland (formerly Perfecto) were both US-based manufacturers whose standard sizes became industry norms. Common sizes such as 10, 20 Long, 29, 55, and 75 gallon often have exterior measurements within a fraction of an inch of each other.
Why does the Fluval Flex calculated volume appear higher than the nominal label volume?
The Flex series has a curved bow-front design. The rectangular L × W × H calculation treats the bow as flat, overstating the true water-holding volume. The actual water volume is less than the rectangular calculation because the curved front displaces volume. Use the Bow Front calculator with the measured bow depth for an accurate result.
Why does the Coralife BioCube hold less display water than the exterior calculation suggests?
The BioCube includes a built-in rear filtration chamber that occupies approximately 20–30% of the tank interior. The exterior volume calculation does not account for this chamber. Always refer to the manufacturer’s stated display volume, or measure inside the display section only.
How do I find the precise water volume of my specific tank?
Measure inside the glass from panel to panel for length and width, and measure to your intended fill line for height. Use the rectangular aquarium volume calculator for a precise result, or visit the measurement guide for step-by-step instructions including how to account for glass thickness, substrate, and fill height.

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