How many liters does an aquarium hold?
Estimate gross water volume and allow for substrate, décor and a safe fill line.
What the calculation represents
Aquarium care depends on actual water volume rather than the nominal tank size. Inside dimensions, water line, substrate and hardscape all matter.
- Reference formula
gross liters = length (cm) × width (cm) × water depth (cm) ÷ 1,000; with inches, multiply the cubic result by 0.016387064- Unit reference
- 1 L = 1,000 cm³ · 1 m³ = 1,000 L · 1 US gal = 231 in³ = 3.785411784 L
A practical workflow
- Measure inside glass length and width and use planned water depth rather than the aquarium’s outside height.
- Calculate gross water volume to that line, listing a sump, rear chamber or external water-holding equipment separately.
- Estimate substrate and hardscape displacement from dimensions or from the measured amount added during setup.
- Create a net range, refine it from the measured water added, and use the best-verified value for dosing; calibrate routine water changes with known-volume buckets or a marked container.
Calculate with your own values
Worked example
A 36 × 12 inch footprint with a 14-inch water depth gives about 99.1 liters gross. Assuming 15 liters of actual displacement for this example leaves about 84.1 liters of water. The unfilled rim is already excluded by using water depth; do not subtract it again.
Estimate the water in your aquarium
For rectangular tanks: enter inside dimensions in centimetres, measuring water depth from the tank bottom to the water surface.
Reading the answer correctly
For treatments, use the best-verified net water volume and follow the product label exactly rather than dosing from the nominal tank size.
Net water volume changes with hardscape and fill level. If displacement in this example lies between 13 and 17 L, water volume is about 82.1–86.1 L. That interval follows the stated assumptions, not a universal aquarium allowance.
Aquarium volume from inside dimensions
These rectangular examples use inside length × width × height in centimeters. The third measurement ends at the waterline; if it reaches the inside rim, the result is capacity to the rim. Substrate, decorations and equipment displacement have not been subtracted. These are metric examples, not nominal US-gallon tank sizes.
Swipe horizontally to see every column
| Inside length (cm) | Inside width (cm) | Measured height (cm) | Geometric volume (L) |
|---|---|---|---|
| 30 | 30 | 30 | 27 |
| 40 | 25 | 25 | 25 |
| 60 | 30 | 30 | 54 |
| 80 | 35 | 40 | 112 |
How many liters does a 30 × 30 × 30 cm aquarium hold?
With inside measurements, 30 × 30 × 30 ÷ 1,000 = 27 liters of geometric volume. If the height reaches the rim, 27 L is capacity to the rim rather than the water in a working setup. At a water depth of 27 cm, the volume is 30 × 30 × 27 ÷ 1,000 = 24.3 L before subtracting decoration and equipment displacement. There is no universal percentage to subtract.
Corner and bow-front aquariums
A right-triangular corner tank can be modeled as a triangular prism. A 60 × 60 cm footprint with 50 cm water depth gives 60 × 60 ÷ 2 × 50 = 90,000 cm³, or 90 L.
For a quarter-circle footprint, use one quarter of a cylinder. An inside radius of 50 cm and 40 cm water depth gives π × 50² ÷ 4 × 40 = 78,540 cm³, approximately 78.54 L.
There is no dependable universal factor for a panoramic or bow-front tank. Split a documented profile into geometric sections, measure the water added during setup, or use the manufacturer’s net-capacity method.
Triangular prism: V = (base × depth ÷ 2) × heightQuarter cylinder: V = (π × radius² ÷ 4) × height
Checks before relying on the number
- Glass thickness, trim and the air gap below the rim are excluded from water volume.
- A sloped substrate bed uses average depth instead of its highest point.
- Sump capacity is counted only to its normal operating level, not to the top of the vessel.
- Treatments follow the product label exactly and use the best-verified net gallons or liters rather than nominal tank size.
Sources and references
These references support the units, method, or limitations explained in this guide.
- NIST — SI Units: Volume
Definitions and exact relationships between liters and cubic units.
- OpenStax — Prealgebra 2e, §9.6
Ideal rectangular-solid, cylinder, sphere and cone formulas; not a certification of product capacity.
- OpenStax — University Physics Volume 1, §14.4
Physical basis of immersion and displaced liquid volume; not treatment-dosing guidance.
Log gross volume, estimated displacement, auxiliary-system water and operating net volume, then revise the record after major aquascape changes.
See how formulas, examples, and updates are reviewed.