125 gallon fish tank: dimensions, weight & setup
A standard 125 gallon tank measures 72 × 18 × 21 inches, holds about 104.4 gallons of real water and weighs roughly 1,145 lb once set up. It is a great size for clown loach groups, large cichlids and show-stopping community tanks.
125 Gallon tank dimensions
| Inches | Centimeters | |
|---|---|---|
| Length | 72 in | 182.9 cm |
| Width (front to back) | 18 in | 45.7 cm |
| Height | 21 in | 53.3 cm |
| Footprint | 1,296 in² (9.0 ft²) | 8,361 cm² |
| Typical glass | 3/8 in | 10 mm |
These are typical outside dimensions for US glass tanks; brands vary slightly, so measure yours before buying a stand, lid or background.
How much water does it really hold?
| US gallons | Liters | |
|---|---|---|
| Outside dimensions | 117.8 | 446.0 |
| Filled 1 in below the rim | 104.4 | 395.3 |
| With 2 in of gravel | 93.8 | 355.0 |
Dose medication and fertilizer for the real water — about 94 gallons once the tank is aquascaped, not 118.
How much does a 125 gallon tank weigh?
| Empty (estimated, 3/8 in glass) | 189 lb | 86 kg |
|---|---|---|
| Filled with fresh water | 1,061 lb | 481 kg |
| Set up, fresh water + 2 in gravel | 1,145 lb | 519 kg |
| Set up as saltwater | 1,164 lb | 528 kg |
| Floor load under the stand | 127 lb/ft² | 6.1 kPa |
Add rock, decor and the stand (often 40–120 lb). A floor load of 127 lb/ft² is 3.2× the 40 lb/ft² a typical home floor is designed for when averaged over a room, so place the stand across the joists and near a load-bearing wall. Use the weight calculator to include your own rock and stand.
Heater size
| Room temperature (water at 78 °F) | Heater |
|---|---|
| 73 °F (5 °F lift) | 2 × 100 W |
| 68 °F (10 °F lift) | 2 × 200 W |
| 63 °F (15 °F lift) | 2 × 250 W |
See the heater size chart by tank or size your own in the heater calculator.
Plan maintenance with the water change schedule: a 30% change on this tank is about 28.1 gallons.
Filter flow
| Tank type | Real flow | Filter rating |
|---|---|---|
| Community tropical | 418–627 GPH | 597–895 GPH |
| Planted tank | 522–835 GPH | 746–1,193 GPH |
| Goldfish, cichlids or heavy feeders | 835–1,044 GPH | 1,193–1,492 GPH |
Substrate
| Depth | Gravel | Sand |
|---|---|---|
| 1 in (2.5 cm) | 71 lb | 69 lb |
| 2 in (5.1 cm) | 142 lb | 138 lb |
| 3 in (7.6 cm) | 213 lb | 206 lb |
Stocking ideas
- 5 clown loaches + 12 rummy-nose tetras + 1 bristlenose pleco
- 1 oscar + 2 bristlenose plecos with room to spare
- 30 harlequin rasboras + 15 corydoras + 3 honey gouramis in a planted layout
Check any combination — including temperature and group size — in the stocking calculator.
Setup tips
- Six feet long and over 1,100 lb set up — ask a contractor about the floor, especially upstairs or in an older home.
- Run two heaters and either a sump or two canister filters at opposite ends.
- Plan water changes with a hose and drain: 30% is around 30 gallons every week.
FAQ
What are the dimensions of a 125 gallon fish tank?
A standard 125 gallon glass tank measures 72 × 18 × 21 inches (182.9 × 45.7 × 53.3 cm) on the outside, a footprint of 9.0 square feet. Brands differ by up to about half an inch.
How much does a 125 gallon fish tank weigh?
About 190 lb empty, 1,060 lb filled with water and roughly 1,145 lb set up with 2 inches of gravel, before rock, decor and the stand.
How many gallons does a 125 gallon tank really hold?
117.8 gallons by its outside dimensions, about 104.4 gallons (395 liters) filled an inch below the rim, and about 93.8 gallons with 2 inches of gravel.
What size heater does a 125 gallon tank need?
2 × 200 W to hold 78 °F in a 68 °F room; 2 × 100 W in a 73 °F room and 2 × 250 W in a 63 °F room.
How much gravel or sand for a 125 gallon tank?
About 71 lb of gravel per inch of depth: 142 lb for a 2-inch bed, or 138 lb of sand.
What filter flow does a 125 gallon tank need?
418–627 GPH of real flow for a community tank (4–6× turnover), so choose a filter rated about 597–895 GPH.