Aquarium Tank Volume Calculator

Aquarium planning tool

Calculate your aquarium’s real water volume

Enter your tank dimensions, then account for the waterline, substrate and hardscape. Results update instantly.

Choose the tank shape

Select the closest geometric shape.

Enter the dimensions

Internal measurements give the most accurate result.

Length cm Width cm Tank height cm

Real-world adjustmentsWaterline, substrate and hardscape

Measurements are

Gap below rim cm Substrate at front cm Substrate at back cm Hardscape & equipment %

Estimated real water volume

—litres

Use this estimate for fertiliser, conditioner and medication dosing.

Gross capacity——

At waterline—Before substrate and hardscape

Water weight—Freshwater estimate

25% water change——

Results are estimates. Measure the inside of the tank for the most accurate result.

How to calculate aquarium volume accurately

Measure the inside length, width and height of your aquarium whenever possible. Internal measurements avoid counting the glass itself, while the waterline setting accounts for the unfilled space below the rim. Select the closest tank shape, enter the dimensions and the calculator will update immediately.

Gross capacity vs real water volume

Gross capacity is the geometric volume of an empty aquarium filled to the brim. Your real water volume is lower because substrate, rocks, driftwood, equipment and the gap below the rim all displace water. The estimated real volume is the more useful number for fertiliser, conditioner, medication and water-change calculations.

Aquarium volume calculator FAQ

Should I measure inside or outside the tank?

Internal measurements are best. If you only have external measurements, choose “External” and enter the glass thickness so the calculator can estimate the internal dimensions.

Which volume should I use for aquarium dosing?

Use the estimated real water volume for most dosing decisions. Always follow the product label and use a conservative estimate when exact displacement is unknown.

Are bow-front and corner tank results exact?

They are geometric estimates because curved aquarium profiles vary by manufacturer. Rectangular, cube and cylindrical calculations are more exact when accurate internal measurements are used.