Works for common tank shapes
Choose rectangular, cylinder, bow-front, or quarter-circle corner tanks and convert the result into liters, US gallons, or UK gallons.
Tools
Aquarium volume calculator
Enter fish tank dimensions to calculate rectangular, cylinder, bow-front, or corner aquarium capacity in liters/litres, US gallons, and UK (Imperial) gallons, with optional adjustments for real water volume.
Use internal dimensions for the most accurate result.
Adjust real water volumeOptional fill-level and displacement corrections
Leave empty for gross volume. Add corrections only when you need a closer estimate of the water actually in the tank.
Useful for water changes
Use the result to estimate partial water change volume, conditioner amount, fertilizer dose, or remineralizer targets.
Account for displacement
Hardscape, substrate, filters, and low fill lines reduce the real water volume compared with external glass dimensions.
Aquarium volume guide
Calculate fish tank volume before stocking, dosing, or changing water.
Aquarium volume, also called fish tank capacity, is the baseline for stocking choices, water changes, medication, fertilizer dosing, filtration planning, and comparing tank sizes. Enter internal tank dimensions, choose liters, US gallons, or UK (Imperial) gallons, then adjust for real water displacement when needed.
How the aquarium volume calculator works
The calculator applies a shape-specific footprint formula, multiplies it by water height, and converts the result into the output unit you choose. Rectangular tanks use length and width, cylinders use diameter, corner tanks use a quarter-circle footprint, and bow-front tanks add a curved segment to the straight-sided area.
For the most practical estimate, use internal measurements. Open the optional advanced settings when a low fill line, substrate, rocks, wood, or equipment noticeably reduces usable water volume.
Rectangular aquarium volume formula and example
For dimensions measured in centimeters, rectangular aquarium volume in liters equals length × width × water height ÷ 1,000. A tank measuring 60 × 30 × 30 cm holds 54 liters before substrate, hardscape, glass thickness, and the fill gap are considered.
The same 54-liter capacity is approximately 14.27 US gallons or 11.88 UK (Imperial) gallons. One US gallon equals about 3.785 liters, while one UK or Imperial gallon equals about 4.546 liters, so the two gallon units must not be treated as interchangeable.
When to use liters, litres, US gallons, or UK gallons
Use liters or litres when dosing products labeled in milliliters per liter, and use gallons when following product labels or water change routines written for US or UK gallons. UK gallon and Imperial gallon mean the same unit; they are larger than US gallons.
If you keep notes in Aquarium Tracker, use the same volume unit each time. That makes parameter logs, maintenance notes, and dosing decisions easier to compare later.
Water change volume planning
Once you know total tank volume, multiply it by your water change percentage. For example, a 100 liter aquarium with a 30 percent water change needs about 30 liters of prepared water.
The real amount can be lower if the tank has a deep substrate bed or large hardscape. If livestock react strongly to water changes, use the calculator result as a planning estimate and observe the tank carefully.
Stocking and filtration context
Volume alone does not decide stocking capacity. Fish size, adult behavior, filtration, surface agitation, plant mass, maintenance habits, and water parameters matter too.
Still, accurate volume helps you avoid comparing a heavily decorated tank with an empty display tank of the same outside dimensions.
FAQ
Aquarium Volume Calculator FAQ
How do I calculate aquarium volume?
For a rectangular tank, multiply length by width by water height. If the dimensions are in centimeters, divide cubic centimeters by 1000 to get liters.
Should I use inside or outside aquarium dimensions?
Inside water dimensions are better for dosing and water changes. Outside dimensions are useful for comparing tanks, but they usually overestimate real water volume.
Does substrate reduce aquarium volume?
Yes. Substrate, rocks, driftwood, internal filters, and decorations displace water, so the real water volume is lower than the empty rectangular tank volume.
What is the difference between US gallons and UK gallons?
A UK gallon is larger than a US gallon. Check which unit a product label or aquarium guide uses before dosing or comparing tank sizes.
Can I use this calculator for bow-front or cylinder tanks?
Yes. Select cylinder and enter diameter plus height, or choose bow-front and enter length, side depth, center depth, and height. Quarter-circle corner tanks are supported too.
How much water should I prepare for a partial water change?
Multiply the estimated aquarium volume by the water change percentage. For example, a 100 liter tank with a 25 percent water change needs about 25 liters of prepared water.
Related aquarium planning
Continue with the next aquarium decision.
Use the calculator result with logs, guides, and maintenance tools so one number becomes part of a repeatable aquarium care routine.
Aquarium Water Change CalculatorTurn tank capacity into a routine change volume or nitrate-reduction amount.Aquarium Dosing CalculatorScale a product-label dose to the actual volume of water being treated.Aquarium Heater Size CalculatorUse the calculated tank volume to estimate practical heater wattage.Aquarium Stocking CalculatorUse adult fish size, water ranges, behavior, and tank volume for an initial stocking review.Aquarium Substrate CalculatorEstimate substrate volume after you know the tank footprint.Water Parameters TrackingTrack pH, KH, nitrate, phosphate, temperature, and more.Aquarium TasksTurn water change volume into recurring maintenance tasks.Aquarium Water Change ScheduleTurn calculated tank volume into a repeatable water-change routine.
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