120 gallon fish tank size and measurements
How big is a 120 gallon tank? It is about 4.0 feet long (48 in), 24 inches from front to back and 24 inches tall, so it needs a stand or space at least 48 x 24 inches.
- Outside dimensions
- 48 x 24 x 24 in121.9 x 61 x 61 cm
- Volume
- 120 US gal454 L, 100 UK gal
- Footprint
- 8.0 sq ft1,152 sq in
- Water weight
- 1,001 lb454 kg
Checked against the manufacturer's specs: the Custom Aquariums 120 gallon measures 48 x 24 x 24 in outside. The size above is the rounded standard size most charts use.
Measured from the outside, these dimensions hold about 119.7 US gallons. Real water volume is lower because of glass thickness, substrate, decor and the gap below the rim. Check the real figure with the aquarium volume calculator.
How much does a 120 gallon tank weigh?
A 120 gallon tank weighs about 1,134 lb of water and gravel, plus the glass, which varies by brand. Use a stand rated for the full weight, on a level floor. The fish tank weight guide compares every size.
How much gravel or sand for a 120 gallon tank?
| Bed depth | Gravel | Sand | Aquasoil |
|---|---|---|---|
| 1 in (2.5 cm) | 67 lb | 63 lb | 19 L |
| 2 in (5.1 cm) | 133 lb | 127 lb | 38 L |
| 3 in (7.6 cm) | 200 lb | 190 lb | 57 L |
Based on a 48 x 24 in floor and typical bulk densities.
Different depth? Use the aquarium substrate calculator.
Heater and filter size for a 120 gallon tank
A common rule is 3–5 watts per gallon, so a 120 gallon tank needs about 360–600 W: two 250 W heaters, spread along the tank suits most rooms. Use the higher end in cold rooms.
For filtration, aim to turn the water over 4–6 times an hour: a filter rated around 480–720 gallons per hour.
Fish that suit a 120 gallon tank
- Reef tanks with corals and reef-safe fish
- Large cichlid communities
- Big schools of rainbowfish or barbs
- Larger plecos suited to the size
Starting ideas only. Check each species' adult size, temperament and water needs before buying.
Compare nearby sizes
- Next smaller: 110 gallon, 48 x 18 x 30 in
- Next larger: 125 gallon, 72 x 18 x 21 in
See every size in the aquarium size chart.
Frequently asked questions
What are the dimensions of a 120 gallon tank?
A standard 120 gallon aquarium measures about 48 x 24 x 24 inches (121.9 x 61 x 61 cm), length x width x height. Brands vary by a fraction of an inch.
How long is a 120 gallon tank?
About 48 inches (121.9 cm), or 4.0 feet.
How big is a 120 gallon tank?
It is about 4.0 feet long, 24 inches deep and 24 inches tall, and takes up 8.0 square feet of floor.
How much does a 120 gallon tank weigh when full?
About 1,134 lb of water and gravel, plus the glass, which varies by brand.
How much gravel do I need for a 120 gallon tank?
For a 2 inch bed, about 133 lb of gravel or 127 lb of sand.
What size heater does a 120 gallon tank need?
About 360–600 watts in total, so two 250 W heaters, spread along the tank suits most rooms.
Last updated .