5 Gallon Tank: Dimensions and Weight
A 5 gallon tank (standard 5.5 gal) measures 16" × 8" × 10.5". It holds about 18.9 liters and weighs about 64 lb full: 7 lb of glass, 42 lb of water and 15 lb of gravel.
Volume
28.05 gal
Liters
106.2 L
This is the full water volume; actual capacity is a bit lower once you add substrate, rocks and the fill line.
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What a 5 gallon tank actually measures
The standard 5.5 gal 5 gallon footprint is 16 × 8 × 10.5 inches inside the glass. Run those through the rectangular formula and you get 5.82 gallons of geometric volume, which is not the same as the 5 on the box. Nominal sizes are round numbers picked for the label; the glass is cut to whatever the mould is. Your real water volume is lower again, because substrate, rock and the inch or two you leave below the rim all come out of it. Budget roughly 10 to 15 percent for a planted tank with a two-inch substrate bed.
How much a 5 gallon tank weighs, empty and full
Water weighs 8.34 lb per US gallon, so 5 gallons is about 42 lb before you add anything. A standard glass 5 gallon weighs about 7 lb empty, and a 2 inch bed of gravel or sand over its 16 × 8 inch floor adds about 15 lb (at 100 lb per cubic foot). All in, that is about 64 lb resting on 0.89 square feet, or 72 lb per square foot. That number, not the gallons, is what decides whether the furniture you were planning to use is a stand or a mistake.
| Component | standard 5.5 gal |
|---|---|
| Empty glass tank | 7 lb |
| Fresh water | 42 lb |
| 2" gravel or sand | 15 lb |
| Total, freshwater | 64 lb |
| Total, saltwater | 65 lb |
| Load on the footprint | 72 lb/sq ft |
Empty weights are typical retail figures for standard glass; check the label on yours. Live rock and hardscape are extra, often 1 to 1.5 lb per gallon on a reef.
What fits in 5 gallons
Each row is the largest single-species group the stocking calculator still rates as comfortable (at or below 85 percent of capacity) in 5 gallons, with adult size and waste output weighted. Species whose minimum tank size is larger than this tank are not listed at all.
| Species | Comfortable group |
|---|
Mixing species changes these numbers; run your actual list through the stocking calculator.
Other standard tank sizes
- 10 gallon tank20" × 10" × 12"
- 20 gallon tank24" × 12" × 16"
- 29 gallon tank30" × 12" × 18"
- 40 gallon tank36" × 18" × 16"
- 55 gallon tank48" × 13" × 21"
- 75 gallon tank48" × 18" × 21"
- 90 gallon tank48" × 18" × 24"
- 125 gallon tank72" × 18" × 21"
Volume by tank shape
- Rectangular tankslength × width × height ÷ 231
- Cube tanksedge³ ÷ 231
- Cylinder tanksπ × (diameter ÷ 2)² × height ÷ 231
- Bowfront tankslength × width × height × 1.06 ÷ 231
- Hexagonal tanks(3√3 ÷ 2) × edge² × height ÷ 231
What to do with the number
- What bioload actually isGallons is the denominator, not the answer
- Cycle the tank firstFishless cycling, step by step
Frequently asked questions
What are the dimensions of a 5 gallon tank?
The standard 5.5 gal footprint is 16 × 8 × 10.5 inches.
How many liters is a 5 gallon tank?
About 18.9 liters (US gallons × 3.785).
How much does a 5 gallon fish tank weigh?
About 64 lb set up: 7 lb for a standard empty glass tank, 42 lb of water (5 gal × 8.34 lb/gal) and about 15 lb for a 2 inch gravel bed. Saltwater adds 1 lb. Rock, the stand and the lid come on top.
How much does an empty 5 gallon tank weigh?
About 7 lb for standard glass. Rimless low-iron glass and acrylic tanks differ: acrylic of the same size is roughly half the weight of glass.
Is a 5 gallon tank really 5 gallons?
Not exactly. Those inside dimensions work out to 5.82 gallons of geometric volume, and the real water volume lands below that once substrate, rock and the gap below the rim are subtracted.
Keep going with the same pet
Got your gallons? Check how many fish that really supports.
Your dog's age in human years, breed-size adjusted, not the ×7 myth.
Your cat's age in human years using the real feline curve, not the ×7 myth.
How much to feed: daily calories and cups by weight, activity and life stage.
Bioload-based stocking guidance, not the oversimplified 1-inch-per-gallon rule.