An aquarium volume calculator determines how much water your fish tank holds. Enter the internal dimensions to get capacity in liters, US gallons, and Imperial gallons.
Aquarium volume is the water-holding capacity of a fish tank. Most aquariums are rectangular prisms, so volume = length × width × height. However, the actual water volume is less than the calculated volume due to glass thickness, substrate (gravel), decorations, and equipment.
A general rule: actual water volume ≈ 85-90% of calculated tank volume. Always measure internal dimensions (inside glass-to-glass) for accurate results.
V = length × width × height (internal dimensions).
Measure in centimeters → divide by 1,000 for liters. Or measure in inches → divide by 231 for US gallons.
Example: 60 cm × 30 cm × 40 cm tank: V = 72,000 cm³ = 72 liters = 19.02 US gal.
After substrate and decorations: usable water ≈ 72 × 0.85 = ~61 liters.
51 × 25 × 30 cm: V = 38,250 cm³ = 38.25 L ≈ 10.1 US gal.
122 × 33 × 51 cm: V = 205,326 cm³ = 205.3 L ≈ 54.2 US gal.
30 × 30 × 35 cm: V = 31,500 cm³ = 31.5 L ≈ 8.3 US gal.
183 × 46 × 56 cm: V = 471,408 cm³ = 471.4 L ≈ 124.5 US gal.
35 free volume calculation tools — click any calculator to get started.
Answers to common questions about the aquarium volume calculator.
Measure L × W × H in inches, then divide by 231 for US gallons (or by 277.42 for Imperial gallons). In cm: multiply L×W×H, divide by 1000 for liters, then by 3.785 for US gal.
Water weighs 1 kg/L (8.34 lbs/US gal). A 100 L tank: water = 100 kg + tank glass ≈ ~115 kg (253 lbs) total. A 55 gal tank ≈ 470 lbs filled.
Use 1-2 inches (2.5-5 cm) of substrate. Volume of gravel = L × W × depth. For a 60×30 cm tank with 3 cm gravel: 60×30×3 = 5,400 cm³ ≈ 5.4 L ≈ 9 kg of gravel.
The old guideline suggests 1 inch of fish per gallon of water. However, this oversimplifies — fish body mass, filtration, and species-specific needs matter more. Modern fishkeeping uses the fish's adult size and bioload instead.
Measure inside the tank from glass to glass (not the outside). Subtract glass thickness from external measurements. Standard aquarium glass is 4-12 mm thick depending on tank size.