125 gallon fish tank size and measurements
How big is a 125 gallon tank? It is about 6.0 feet long (72 in), 18 inches from front to back and 21 inches tall, so it needs a stand or space at least 72 x 18 inches.
- Outside dimensions
- 72 x 18 x 21 in182.9 x 45.7 x 53.3 cm
- Volume
- 125 US gal473 L, 104 UK gal
- Footprint
- 9.0 sq ft1,296 sq in
- Water weight
- 1,042 lb473 kg
Measured from the outside, these dimensions hold about 117.8 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 125 gallon tank weigh?
A 125 gallon tank weighs about 1,398 lb (634 kg) once set up, counting the empty glass (206 lb), the water and 2 inches of gravel. 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 125 gallon tank?
| Bed depth | Gravel | Sand | Aquasoil |
|---|---|---|---|
| 1 in (2.5 cm) | 75 lb | 71 lb | 21 L |
| 2 in (5.1 cm) | 150 lb | 142 lb | 42 L |
| 3 in (7.6 cm) | 225 lb | 214 lb | 64 L |
Based on a 72 x 18 in floor and typical bulk densities.
Different depth? Use the aquarium substrate calculator.
Heater and filter size for a 125 gallon tank
A common rule is 3–5 watts per gallon, so a 125 gallon tank needs about 375–625 W: two 250 W heaters, one at each end 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 500–750 gallons per hour.
Fish that suit a 125 gallon tank
- African cichlids
- Large rainbowfish and barb groups
- Larger community fish
- Marine fish-only or reef setups
Starting ideas only. Check each species' adult size, temperament and water needs before buying.
Compare nearby sizes
- Next smaller: 100 gallon, 72 x 18 x 18 in
See every size in the aquarium size chart.
Further reading
Frequently asked questions
What are the dimensions of a 125 gallon tank?
A standard 125 gallon aquarium measures about 72 x 18 x 21 inches (182.9 x 45.7 x 53.3 cm), length x width x height. Brands vary by a fraction of an inch.
How long is a 125 gallon tank?
About 72 inches (182.9 cm), or 6.0 feet.
How big is a 125 gallon tank?
It is about 6.0 feet long, 18 inches deep and 21 inches tall, and takes up 9.0 square feet of floor.
How much does a 125 gallon tank weigh when full?
About 1,398 lb (634 kg) once set up, counting the empty glass (206 lb), the water and 2 inches of gravel.
How much gravel do I need for a 125 gallon tank?
For a 2 inch bed, about 150 lb of gravel or 142 lb of sand.
What size heater does a 125 gallon tank need?
About 375–625 watts in total, so two 250 W heaters, one at each end suits most rooms.
Last updated .