Fish Tank Gallon Calculator: Convert Dimensions to Gallons
Fish Tank Gallon Calculator: Convert Dimensions to Gallons
Every gallon calculator starts from the same conversion: 1 US gallon = 231 cubic inches. For a rectangle, that's (length × width × height in inches) ÷ 231. A cylinder is (π × radius² × height) ÷ 231. A bow-front adds an elliptical bulge to a rectangle. Most calculators stop there, at volume. They don't tell you whether the tank's footprint actually sits on a living-room stand.
Every wood aquarium stand in Burlholt's aquarium stand collection is solid hardwood - no veneer, no MDF - listed at 16" deep across every size. Gallons don't buy a stand; outside tank length and width do. If the tank is deeper than 16", it overhangs - don't use these tops for that tank.
How to Measure Before You Divide
- For gallons (dosing, salt, stocking): measure the water column - inside length, inside width, and the height of the water, not the rim. True water volume commonly runs 10-20% under the box label once substrate, rock and the gap below the rim are accounted for.
- For a stand: measure the tank's outside length and width, including the frame. Stand width needs to be at least the tank's length; stand depth needs to be at least the tank's width. Every listed Burlholt size is 16" deep.
- US vs liters. Liters ≈ US gallons × 3.785. UK (imperial) gallons are larger, based on roughly 277 cubic inches - this article uses US gallons throughout.
- Water mass is not a stand rating. Freshwater runs close to 8.34 lb per US gallon before glass, substrate and rock are added. Use that only as a planning reminder - see the weight-rating note above for what it does and doesn't tell you about a specific stand.
Rectangle calculator. Enter inches. If JavaScript is off, use the formula under the fields.
US gallons ≈ 10.39 · liters ≈ 39.3
Formula: gallons = (L × W × H) ÷ 231. Then liters = gallons × 3.785.
Rectangular Tank (the Standard Box)
This is the shape every "10 / 20 / 29 / 55" label assumes. Worked example: 20" × 12" × 10" = 2,400 cu in ÷ 231 ≈ 10.39 US gallons. A second example: 24" × 12" × 16" = 4,608 ÷ 231 ≈ 19.95 gallons.
How to calculate it: tape inside L, W, and water height. Multiply, divide by 231. For the stand, switch to outside L × W. A 10-gallon class tank commonly runs close to 20" × 10" - 10" of depth clears 16"D easily. A 20-long or 29-gallon class commonly runs closer to 30" × 12".
Listed match (10-gal class): Rustic Cabinet Living Room Corner, sizes 20", 24", 30", 35", 39", 43"W (all 51"H × 16"D), from $1,680. Solid hardwood, not a particle-board cube.
Listed match (20-long / 29 class): same rustic cabinet at 30"W, or seating height on the Elegant Coffee Table With Built, sizes 35", 39", 43", 47", 51", 55"W (all 31"H × 16"D), from $2,080.
Cube
A cube is edge³, then ÷ 231 if measured in inches. A 16" cube is 4,096 ÷ 231 ≈ 17.7 gallons. Outside depth on a 16" cube is exactly the listed Burlholt cap, not a margin - confirm the actual outside dimension, since glass thickness can push a nominal "16-inch cube" past 16" once measured.
How to choose a stand: only proceed if outside width is confirmed ≤16" and outside length fits within a listed width. 16" of tank on 16" of top is a flush fit, not extra wood - prefer a closed cabinet so filters aren't hanging off the edge of a cube-shaped tank.
Listed match: rustic cabinet at 20"W, from $1,680, if the cube's outside length is ≤20" and outside depth is confirmed ≤16". If the cube measures deeper than 16", this collection isn't the right fit.
Cylinder (and Half-Cylinder)
Formula: gallons = (π × r² × H) ÷ 231, with r = diameter ÷ 2. A half-cylinder is that result, divided by 2. Example: diameter 12", height 18" → π × 6² × 18 ÷ 231 ≈ 8.8 gallons.
How to match a stand: the footprint is a circle, so the stand needs to cover the full diameter in both directions. A 12" diameter cylinder clears 16"D; an 18" diameter one does not. Don't let the curve overhang the front edge.
Listed match: the Cozy Living Room Rustic Floating Shelf at 18"W (1.5"T × 16"D), from $560, for a small cylinder whose diameter is ≤16". For a floor case, the rustic cabinet at 20"W, from $1,680.
Bow-Front
A bow-front's volume is roughly the rectangle area (L × W) plus an elliptical bulge, π × (L ÷ 2) × (full width − W) ÷ 2, then multiplied by height and divided by 231. The number that matters for a Burlholt top is full width - the deepest point of the bow, not the flat back panel's width.
How to choose: if full width is over 16", the bow overhangs every stand in this collection. Many 36" bow-fronts are actually built for 18-20"-deep cabinets, so don't force one onto 16"D. If you have a shallow bow whose full width measures ≤16", treat it like a rectangle of that full width and pick a listed width at or above the tank's length.
Listed match (only if full width is confirmed ≤16"): the With Canopy Living Room stand at 39"W (51"H × 16"D), from $2,600, for a roughly 30-36" long tank that still clears the depth cap.
55-Gallon Class (~48" × 13") vs. Tanks That Fail 16"D
A nominal 55-gallon commonly runs close to 48" × 13" × 21". Volume check: 48 × 13 × 21 = 13,104 ÷ 231 ≈ 56.7 gallons of empty glass. Depth around 13" clears 16"D with margin; length around 48" needs a listed width of at least 51".
A 40-breeder (roughly 36" × 18") and a 75-gallon (roughly 48" × 18") both calculate to a lot of water and both fail the 16" depth cap. Past that point, the gallon number stops mattering - depth alone rules them out.
Listed match (55-class, only if your tape confirms depth ≤16" and length ≤51"): canopy at 51"W, from $2,600, or the Elegant Stylish Living Space at 51"W (51"H × 16"D), from $3,000. For seated viewing, the coffee-table's 51"W size, from $2,080.
Where Volume Calculators Stop and Fit Begins
Standard calculators handle rectangle, cube, cylinder, bow-front and hex shapes, US-vs-liters conversion, and the 10-20% "actual water" adjustment for dosing. What they generally don't do is map the resulting footprint onto a piece of furniture. This article keeps the standard formulas, then applies Burlholt's actual catalog constraint: 16" depth across every size, widths from 18" (the smallest shelf) up to 71" (the largest canopy), four finishes (Black, Oak, Brown, Walnut), and solid timber construction so a spill doesn't behave like particle board.
Quick Pairing Chart
| Shape / class | Gallon math (inches ÷ 231) | Fits listed 16"D? | Burlholt form to check |
|---|---|---|---|
| Rectangle ~10 gal | 20 × 10 × 12 → ≈10.4 gal | Yes (10" deep) | Rustic cabinet, 20"W - from $1,680 |
| Rectangle 20-long / 29 | 30 × 12 × 13 → ≈20.3 gal; ×19 → ≈29.6 gal | Yes (12" deep) | Cabinet 30"W or coffee-table 35"W |
| Cube 16" | 16³ ÷ 231 → ≈17.7 gal | Only if outside depth confirmed ≤16" | Rustic cabinet, 20"W |
| Cylinder 12" dia × 18"H | π × 6² × 18 ÷ 231 → ≈8.8 gal | Yes | Floating shelf 18"W or cabinet 20"W |
| Bow-front | rectangle + elliptical bulge | Only if full width ≤16" | Canopy, 39"W |
| 55-class | 48 × 13 × 21 → ≈56.7 gal | Yes (13" deep) | Canopy or stylish, 51"W |
| 40-breeder / 75-gal | — | No (≈18" deep) | None of these tops |
Frequently Asked Questions
Why does my tank's gallon label not match what the calculator gives me?
Gallon labels are nominal, rounded marketing numbers based on outside dimensions and glass thickness assumptions that vary by manufacturer. The calculator uses your actual measured inside dimensions, so a small difference between the two is normal - trust your own measurement for both dosing and stand-fit decisions.
Does knowing my tank's gallon volume tell me which stand fits?
No, not on its own. Two tanks with the same gallon label can have very different footprints - a 20-gallon high and a 20-gallon long differ by several inches in both length and width. Always check outside length and width (and especially depth) separately from the gallon number.
My bow-front tank is 36 inches long - will it fit a 16 inch deep stand?
Only if the bow's full width - the deepest point of the curve, not the flat back panel - measures 16 inches or less. Many 36-inch bow-fronts are built for 18-20 inch deep cabinets specifically because of that curve, so measure the actual bulge before assuming it fits.
Is there a published weight rating I can check my calculated gallon total against?
Not currently, in pounds, on Burlholt's product pages - they describe the build as solid hardwood rated for a filled tank but don't publish a specific figure. Use the gallon-to-weight math here for your own planning, and for a large or wall-mounted setup, contact Burlholt directly with your filled weight before ordering.
Do UK gallons give a different result than this calculator?
Yes. This calculator uses US gallons (231 cubic inches). An imperial (UK) gallon is larger, based on roughly 277 cubic inches, so the same tank volume will show a smaller number of imperial gallons than US gallons. Convert explicitly rather than assuming the two are interchangeable.
Explore Burlholt's Wood Aquarium Stands
Calculate your tank's volume for dosing and stocking, then separately measure its outside footprint for the stand - the two numbers answer different questions. Keep depth at or under 16" and match width to the tank's length before you order.
