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Aquarium Volume Calculator

Computes the water volume of a rectangular fish tank from its internal length, width and height (cm or inches), the weight of that water (fresh or marine), a float-glass side-pane thickness estimate by Stilwell's method, and the '1 inch of fish per gallon' stocking heuristic.

When to use

You are planning or filling a rectangular aquarium and need its capacity, the load on a stand or floor, a glass-thickness ballpark or a rough stocking limit.

Do not use when: The tank is bow-front, cylindrical or hexagonal (compute the footprint area separately), or you need a swimming-pool volume (use pool-volume).

Formula

water_height = height × fill_percent / 100; V = length × width × water_height (cm³ / 1000 = L; in³ × 0.016387 = L); US gal = L / 3.785411784; UK gal = L / 4.54609; glass t_mm = √(β × H_mm³ × 0.00001 / 5.05), β by length/height ratio: 0.5 → 0.2419, 1 → 0.294, 1.5 → 0.325, 2 → 0.3415, 2.5 → 0.35, 3 → 0.37 (interpolated, clamped); stocking = US gallons × 1 inch

The glass formula is Warren Stilwell's method for a side pane supported on three edges: allowable stress 5.05 N/mm² (19.2 N/mm² tensile strength of annealed glass ÷ safety factor 3.8) under hydrostatic load. The 1-inch-per-gallon rule ignores fish body mass, activity and filtration and overstocks tanks with fish over about 3 inches; use it only as a first sanity check.

Inputs

ParameterTypeUnitRequiredDescription
lengthnumberyesInternal length of the tank. Range: > 0, ≤ 2000
widthnumberyesInternal width. Range: > 0, ≤ 2000
heightnumberyesInternal height (water height when full). Range: > 0, ≤ 2000
unitenum: cm | indefault cmUnit of the three dimensions.
fill_percentnumber%default 100Water height as a percentage of the tank height (allow for the air gap and substrate). Range: ≥ 10, ≤ 100

Outputs

OutputTypeUnitDescription
volume_litersnumberLlength × width × water height.
volume_gallons_usnumberUS galSame volume in US gallons (3.7854 L).
volume_gallons_uknumberUK galSame volume in imperial gallons (4.5461 L).
water_weight_kgnumberkgVolume × 0.998 kg/L (fresh water at 20 °C), excluding glass, substrate and rock.
seawater_weight_kgnumberkgVolume × 1.025 kg/L for marine tanks.
glass_thickness_estimate_mmnumbermmSide-pane float glass thickness from t = √(β × H³ × 0.00001 / 5.05) with safety factor 3.8 (H = water height in mm).
recommended_glass_mmintegermmNext standard sheet thickness (4, 5, 6, 8, 10, 12, 15, 19 mm) at or above the estimate.
stocking_inches_of_fishnumberinches of fishTotal adult length of small fish by the 1 inch per US gallon heuristic (rough guide only).

Example

100 × 40 × 50 cm tank: {"length":100,"width":40,"height":50,"unit":"cm"} → {"volume_liters":200,"volume_gallons_us":52.8,"volume_gallons_uk":44,"water_weight_kg":199.6,"seawater_weight_kg":205,"glass_thickness_estimate_mm":9.2,"recommended_glass_mm":10,"stocking_inches_of_fish":52.8}

48 × 13 × 21 in ('55 gallon'): {"length":48,"width":13,"height":21,"unit":"in"} → {"volume_liters":214.7,"volume_gallons_us":56.7,"volume_gallons_uk":47.2,"water_weight_kg":214.3,"glass_thickness_estimate_mm":10.2,"recommended_glass_mm":12}

GET https://tttkmbb.com/api/v1/calculate/aquarium-volume?length=100&width=40&height=50&unit=cm

Machine access

Sources

FAQ

Why is my '55 gallon' tank only 52 gallons here?

Trade names use nominal external sizes; internal dimensions, the air gap and substrate reduce real water volume by 10–15%. Enter internal measurements and a fill_percent below 100 for the actual amount.

Can I rely on the glass thickness estimate?

It is a ballpark for annealed float glass panes with a rim and no bracing; manufacturers often use thinner glass with braces and thicker glass for tanks over 60 cm high. Check with the glass supplier or a dedicated calculator before building.

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