Enter tank dimensions and shape to estimate gross geometric volume in US gallons and liters. The runtime also estimates water weight and glass weight. It does not calculate net water volume or include substrate, hardscape, equipment, or stand weight in the filled-weight output.
How volume is calculated
For a rectangle, the calculator multiplies entered length, width, and height in inches and divides by 231. For a cylinder, it calculates π times radius squared times height, then divides by 231. Liters are estimated by multiplying gross gallons by 3.78541. These are geometric estimates based on the dimensions entered.
Gross volume and usable water
Gross geometric volume is not the same as the amount of water in an operating aquarium. Internal dimensions, glass thickness, the waterline, substrate, rocks, decor, and equipment can reduce actual water volume. The calculator does not apply a fixed displacement percentage or estimate those deductions; measure the actual water volume or make a separate setup-specific estimate when accuracy matters for dosing.
Explicit Stepped Arithmetic: 40-Gallon Breeder Case Study
To eliminate calculation ambiguity, examine how external dimensions translate into true usable water volume and structural weight for a standard 40-Gallon Breeder aquarium:
Given Parameters:
• External Dimensions: Length = 36.0 in, Width = 18.0 in, Height = 16.0 in
• Glass Thickness = 0.25 in (6 mm) | Top Waterline Gap = 1.5 in
• Hardscape & Substrate Displacement = 12% average
Step 1: Gross External Geometric Volume
Gross Volume (gal) = (36 × 18 × 16) ÷ 231 = 10,368 ÷ 231 ≈ 44.88 US Gallons (169.9 Liters)
Step 2: Net Usable Water Volume (Internal Dimensions & Displacement)
Internal Length = 36.0 − (0.25 × 2) = 35.5 in
Internal Width = 18.0 − (0.25 × 2) = 17.5 in
Internal Water Height = 16.0 − 1.5 = 14.5 in
Internal Volume = (35.5 × 17.5 × 14.5) ÷ 231 = 9,008.1 ÷ 231 ≈ 39.00 Gallons
Net Usable Water = 39.00 × (1 − 0.12) = 39.00 × 0.88 ≈ 34.32 Gallons (129.8 Liters)
Step 3: Three-Tier Weight Breakdown
Net Water Weight = 34.32 gal × 8.34 lbs/gal ≈ 286.1 lbs (129.8 kg)
Glass Tare Weight ≈ 52.0 lbs (23.6 kg)
Substrate + Hardscape Weight ≈ 45.0 lbs (20.4 kg)
Total Static Filled Load ≈ 286.1 + 52.0 + 45.0 = 383.1 lbs (173.8 kg)
Weight estimate and exclusions
The displayed empty-weight estimate is based on a rough volume-based glass-weight assumption. Filled weight adds estimated water weight at 8.34 lb per US gallon to that estimated glass weight. It excludes substrate, hardscape, equipment, and stand. Use verified component weights for a complete installed-weight estimate.