How do I calculate aquarium water volume accurately?

Start with the internal cavity: internal width = external width − 2× glass thickness, internal depth = external depth − 2× glass thickness, effective water depth = running water level − base pane thickness. Multiply the three and divide by 1e6 to get litres, then deduct the substrate volume.

How much water does a 120×50×50 tank hold?

With 12mm glass, a 475mm water level and 50mm of substrate, the internal cavity is 1176×476mm with an effective water depth of 413mm: about 231L brim-full, or about 203L once the substrate is deducted.

How heavy is an aquarium once substrate is added?

For a 120×50×50 with 12mm glass: roughly 65kg of glass, 203kg of water and 45kg of substrate (5cm, about 28L) — about 313kg in total, before the stand and hardscape are added.

How large an aquarium can a floor take?

Typical residential floor live load design is 200~300 kg/m². A 1.2×0.5m tank has a 0.6m² footprint, so a 320kg total works out to about 533 kg/m², clearly above domestic loading; place it against a load-bearing wall or beam and use a full base board to spread the load.

Why does my tank take less water than the calculated figure?

Common reasons: substrate and hardscape displace volume, the water is not filled to the rim, filter chambers and pipework hold water too, and the glass is thicker than its nominal figure.

C-02

Water Volume

When a shop labels a tank "120", that is the outside dimension. The real water volume has to subtract the glass thickness, the water gap and the substrate. On a 120 tank with 5cm of substrate, the true volume can be more than 60L below the external volume.

Work aquarium water volume out from the internal clear dimensions: using the outside dimensions overstates it by 5%~15%.

Units

Input parameters

Outer length Win

Outer depth Din

Outer height Hin

Water gap below rimin

Substrate thicknessin

Glass thickness (0 = auto)in

Auto-recommended 0.31 in (bottom 0.39 in)

Aquascaping stone / driftwood weightlb

Load bearing conversion

Operating water (minus substrate): 40 US gal
Full water (to the rim): 44.6 US gal
Substrate volume: 3 US gal
Inner clear dimensions: 34.8 × 17.09 × 16.73 in
Glass weight: 69.6 lb
Water weight: 334.1 lb
Substrate weight (approx.): 40.6 lb
Total tank weight (approx.): 444.3 lb

Based on a footprint of 4.4 ft², the average floor load is about 102 lb/ft². Typical residential floor design live load is 41 lb/ft² (living rooms) to 61 lb/ft²; place large tanks against a load-bearing wall or beam and use a full-size base mat to spread the pressure.

Water weight is taken as 8.3 lb/US gal; aquasoil and river sand bulk density estimated at about 13.4 lb/US gal
Glass density taken as 156 lb/ft³ (2.507 for low-iron)
Stand, filtration and equipment weights are not included; allow another 15%~25% margin in practice

The calculator above follows the unit system selected at the top of this page; the explanatory text below stays metric (mm / L / kg / ℃).

Need a full design?

Want to turn the dimensions into a 3D model and a complete bill of materials: Enter length, width and height in the aquarium designer and it generates the 3D model, dimensions, glass cut list, silicone usage and equipment selection, all exportable as CSV and PNG.

How to use it

Step 1Enter external dimensions and glass thicknessLeave the thickness at 0 to have it recommended from the water height, or enter the actual glass thickness.
Step 2Enter the water gap and substrate depthSubstrate is deducted directly from the usable water volume, and it shows up most on aqua soil tanks.
Step 3Read the net volume and total tank weightTotal weight covers glass, water, substrate and hardscape, and is what you check floor loading and the need for a base board against.

Frequently asked questions

How do I calculate aquarium water volume accurately?: Start with the internal cavity: internal width = external width − 2× glass thickness, internal depth = external depth − 2× glass thickness, effective water depth = running water level − base pane thickness. Multiply the three and divide by 1e6 to get litres, then deduct the substrate volume.
How much water does a 120×50×50 tank hold?: With 12mm glass, a 475mm water level and 50mm of substrate, the internal cavity is 1176×476mm with an effective water depth of 413mm: about 231L brim-full, or about 203L once the substrate is deducted.
How heavy is an aquarium once substrate is added?: For a 120×50×50 with 12mm glass: roughly 65kg of glass, 203kg of water and 45kg of substrate (5cm, about 28L) — about 313kg in total, before the stand and hardscape are added.
How large an aquarium can a floor take?: Typical residential floor live load design is 200~300 kg/m². A 1.2×0.5m tank has a 0.6m² footprint, so a 320kg total works out to about 533 kg/m², clearly above domestic loading; place it against a load-bearing wall or beam and use a full base board to spread the load.
Why does my tank take less water than the calculated figure?: Common reasons: substrate and hardscape displace volume, the water is not filled to the rim, filter chambers and pipework hold water too, and the glass is thicker than its nominal figure.