Aquarium Weight Calculator
Estimate how much your aquarium weighs once it is set up and full: water, glass, substrate, rock and stand. It also shows the load on the floor under the tank, so you know whether to think twice about where it goes.
How to use this calculator
- Enter the outside dimensions of the tank and the glass thickness. The calculator works out the inside size from these.
- Enter how far below the rim the water sits. Most tanks are filled 1 to 2 inches (2.5 to 5 cm) short of the top.
- Add the substrate, rock and stand. These are easy to forget, and on a reef tank the rock alone can add 50 to 100 pounds. Leave the stand at zero if you only want the weight sitting on the stand.
Formulas used
Glass weight = glass volume × 2.5 g/cm³
Floor load = total ÷ (L × W)
Here L, W and H are the outside dimensions, t is the glass thickness, and the glass formula counts a bottom panel, front and back, and two ends. It treats each panel as full size, which slightly overcounts the overlapping edges and roughly balances out the silicone and trim it leaves out.
Fresh water at 25°C weighs 0.997 kg per liter (8.32 lb per US gallon). Seawater at 35 ppt and 25°C is 1.0236 kg per liter (8.54 lb per gallon).
The water figure is a little high on purpose: substrate and rock push some water out, but for a weight check it is safer to round up.
Worked example: 55 gallon freshwater tank
A 55 gallon tank measures 48 × 13 × 21 inches outside. Assume 1/4 inch glass, water 1 inch below the rim and 80 lb of gravel:
- Inside water space = 47.5 × 12.5 × 19.75 inches = 192.2 liters (50.8 gallons)
- Water = 192.2 × 0.997 = 191.6 kg = 422 lb
- Glass = 0.25 × (624 + 2,016 + 546) = 796.5 cubic inches × 2.5 g/cm³ = 72 lb
- Total with gravel = 422 + 72 + 80 = 574 lb (260.5 kg)
- Footprint = 48 × 13 inches = 4.33 ft², so the load is 133 lb per ft²
In metric: a 120 × 50 × 50 cm tank with 10 mm glass, water 3 cm below the rim, 40 kg of sand, 20 kg of rock and a 30 kg stand weighs about 407 kg, or 679 kg per square meter of footprint.
Will my floor hold it?
US building codes design most residential floors for a uniform live load of 40 pounds per square foot, and the IRC allows 30 psf in sleeping rooms. That number is an average spread over the whole room. It is not a limit for one spot, and every full aquarium goes far beyond 40 psf on its own footprint, as the 133 psf in the example shows.
Floors handle most small and medium tanks fine because the joists share the load and the rest of the room is lightly loaded. Boise Cascade's engineering note on residential floor loads says that if an object full of water "weighs more than the 40 psf uniform load placed over its footprint, the floor joists or beams should be designed for the heavier load." An aquarium is also a constant load, unlike people moving around.
Common-sense placement helps: set heavy tanks near a load-bearing wall rather than mid-span, orient the stand so it crosses several joists, and make sure it sits flat and level.
Approximate full weights
Freshwater, 1/4 inch glass (3/8 inch for 75 and 125 gallon), water 1 inch below the rim, no substrate or stand. Calculated with the formulas above.
| Tank | Outside size (in) | Water + glass |
|---|---|---|
| 10 gallon | 20 × 10 × 12 | about 93 lb |
| 20 gallon long | 30 × 12 × 12 | about 162 lb |
| 29 gallon | 30 × 12 × 18 | about 247 lb |
| 40 gallon breeder | 36 × 18 × 16 | about 384 lb |
| 55 gallon | 48 × 13 × 21 | about 494 lb |
| 75 gallon | 48 × 18 × 21 | about 699 lb |
| 125 gallon | 72 × 18 × 21 | about 1,041 lb |
Frequently asked questions
How much does a 55 gallon fish tank weigh when full?
A typical 55 gallon glass tank with about 51 gallons of fresh water, 1/4 inch glass and 80 pounds of gravel comes to roughly 575 pounds, before the stand. With rock, a stand and equipment, 650 to 700 pounds is realistic.
Can my floor hold a big aquarium?
Most US homes are designed for a uniform live load of 40 pounds per square foot. A full aquarium puts far more than that on its own footprint, which ordinary floors usually handle for small and medium tanks because the load is shared by several joists. For large tanks, upper floors or older homes, have a structural engineer or contractor check the floor.
Is saltwater heavier than freshwater?
Yes, slightly. Seawater at reef salinity (35 ppt) is about 1.024 kg per liter at 25°C, compared with about 0.997 for fresh water, so a saltwater tank's water weighs roughly 2.7 percent more.
How accurate is the glass weight estimate?
It adds up the five glass panels using a density of 2.5 grams per cubic centimeter, which is the standard reference value for soda-lime float glass. Bracing, trim and silicone are not included, so the real empty tank may weigh a little more. Use the manufacturer's empty weight if you have it.
Where should I put a heavy aquarium?
Close to a load-bearing wall is generally better than the middle of a room, and placing the tank so it spans several floor joists spreads the load. Make sure the stand sits flat and level on a solid surface.
Related calculators
- Aquarium volume calculator: gallons and liters for any shape
- Substrate calculator: how much your gravel or sand weighs
- Glass thickness calculator: how thick the glass should be
Sources: Residential floor design loads from Boise Cascade Tech Note IJ-12, Design Live Loads for Residential Floors. Glass density of 2.5 g/cm³ from soda-lime glass reference data (measured values 2.44–2.53). Seawater density of 1023.6 kg/m³ at 25°C and 35 g/kg from seawater reference data. Fresh water density from USGS Water Science School.
Last updated: October 2026