Water is heavy: 8.34 pounds per US gallon, or exactly one kilogram per liter. That means even a modest 29-gallon tank carries well over 200 pounds of water, and a 75-gallon tank ends up heavier than a baby grand piano once glass, gravel and rock are added. Knowing the real weight helps you choose a stand, a room and a spot on the floor before the tank is full — when moving it is no longer an option.
Weight chart for standard tanks
The table below is computed from each tank's outside dimensions and typical glass thickness. "Filled" is water to an inch below the rim with no substrate. "Set up" adds a 2-inch gravel bed (with the water held between the grains) and accounts for the water it displaces. Neither includes rock, decor or the stand.
| Tank | Empty | Filled | Set up |
|---|---|---|---|
| 5 gallon | 8 lb | 47 lb | 55 lb (25 kg) |
| 10 gallon | 11 lb | 87 lb | 100 lb (45 kg) |
| 15 gallon | 21 lb | 129 lb | 148 lb (67 kg) |
| 20 gallon high | 27 lb | 174 lb | 193 lb (87 kg) |
| 20 gallon long | 25 lb | 160 lb | 184 lb (83 kg) |
| 29 gallon | 35 lb | 244 lb | 268 lb (121 kg) |
| 40 gallon breeder | 59 lb | 390 lb | 433 lb (196 kg) |
| 40 gallon long | 62 lb | 353 lb | 391 lb (177 kg) |
| 55 gallon | 79 lb | 503 lb | 544 lb (247 kg) |
| 65 gallon | 121 lb | 618 lb | 659 lb (299 kg) |
| 75 gallon | 135 lb | 713 lb | 769 lb (349 kg) |
| 90 gallon | 150 lb | 816 lb | 872 lb (396 kg) |
| 125 gallon | 189 lb | 1,061 lb | 1,145 lb (519 kg) |
| 150 gallon | 315 lb | 1,470 lb | 1,553 lb (704 kg) |
Part 1: the water
Fresh water weighs 8.34 lb per US gallon at room temperature — the difference between 60 °F and 80 °F water is less than half a percent, so temperature can be ignored. Saltwater is denser: at a specific gravity of 1.025, the level most reef tanks run at, it weighs about 8.55 lb per gallon. A 75-gallon reef therefore carries around 13 lb more water than the same tank running freshwater.
Use the real water volume, not the tank's nominal size. A "55" filled an inch below the rim with 2 inches of gravel holds about 46 gallons of water — 380 lb, not the 459 lb you get from 55 × 8.34. The weight does not vanish, though: it moves into the gravel.
Part 2: the glass
Glass weighs about 2.5 kg per liter, or 156 lb per cubic foot. An empty tank's weight is roughly the area of its five panels × thickness × density, plus about 10% for the plastic frame, silicone and center braces. Thickness grows with height because water pressure grows with depth: small tanks use about 1/8 inch, a 55 about 1/4 inch, and 75–125 gallon tanks 3/8 inch or more. Rimless "low-iron" tanks often use thicker glass than framed ones of the same size and weigh more.
Acrylic tanks are about half the density of glass and usually lighter despite thicker walls, which is one reason very large and oddly shaped aquariums are made from acrylic.
Part 3: substrate, rock and decor
Dry aquarium gravel weighs about 100 lb per cubic foot. Once wet, about a third of the bed's volume is water, adding roughly another 20 lb per cubic foot. A 2-inch gravel bed in a 75-gallon tank weighs about 95 lb dry and over 110 lb wet. Rock is the wild card: reef keepers commonly add 1–1.5 lb of live rock per gallon, and a Lake Malawi cichlid tank can carry 100 lb or more of stacked rock. Driftwood and plants are light by comparison.
Part 4: the stand and equipment
A metal stand weighs 20–40 lb, a wooden cabinet 40–120 lb, and a sump with water, return pump and plumbing can add another 100–250 lb on a reef. Include them when you think about the floor.
What it means for your floor
Floor load is weight divided by area. A set-up 55-gallon tank of about 545 lb sits on a stand only 48 × 13 inches — 4.3 square feet — so it presses down at roughly 125 lb per square foot. US homes are typically designed for a live load of 40 lb per square foot, but that figure is an average across a whole room; floors carry concentrated loads such as bathtubs, pianos and bookcases all the time because joists spread them out.
- Run the tank across the joists, not parallel to them, so its weight is shared by as many joists as possible.
- Place it near a load-bearing wall, where joists are supported, rather than in the middle of a span.
- Ground floors and slabs are the safest place for anything over 75 gallons. A concrete slab can carry almost any home aquarium.
- Upstairs, older homes and very large tanks (125 gallons and up) deserve an opinion from a structural engineer or contractor. It is a small cost compared with water damage.
- Renters should check their lease: many limit water beds and aquariums by gallons.
Watch for warning signs after setting up: doors that start sticking, cracks in drywall near the tank, or a level that shows the stand tilting over the first weeks.
Never move a full tank
Glass tanks are designed to be supported evenly on their bottom frame. Lifting or sliding a tank with water inside twists the frame and stresses the silicone seams, and the water's weight is far beyond what two people can safely carry. Drain it to a few inches, remove fish into buckets, and then move it — or better, drain it fully.
Work out your own tank
The aquarium weight calculator adds water, glass, wet substrate, rock and stand for any dimensions and shows the floor load. For standard sizes, see the tank size chart.