How many gallons does a 5.5 gallon tank hold?
16 × 8 × 10 in · freshwater planning
5.5 gallon · tank volume
First decisions for this nano setup
On a 16-inch nano tank, small measurement errors matter. Half an inch of missing height represents 0.28 gallons before allowing for glass. Measure the waterline rather than assuming a full rim-height fill. A measured refill container is a useful check once substrate is in place.
Assumptions and limits
Geometric volume uses the listed planning dimensions. Glass, the fill line, substrate and decor reduce usable water; 80–90% is only a rough range. A nominal name is not a measurement.
5.5 gallon equipment and layout plan
A rectangular layout supports a straight front swimming lane and a rear equipment zone. The 16 × 8-inch base has an aspect ratio of 2:1. A lid or light must span roughly 16 inches; measure rim openings and bracket adjustment before ordering.
| Volume interpretation | US gallons |
|---|---|
| Marketed nominal size | 5.5 |
| Rounded rectangle, before glass | 5.54 |
| Inside panes, brim full model | 5.06 |
| Inside panes, 1 inch below rim | 4.55 |
| 2-inch bed envelope, before decor | 1.11 |
Using 0.19-inch glass, the inner model holds 5.06 gallons, a loss of 0.48 from the rounded rectangle. That loss matters when a small nominal label is close to a livestock minimum. Verify the operating fill directly; do not count substrate pore space as empty air.
Compared with the 5 gallon, this layout has the same 5.54 geometric gallons before glass. Extra nominal capacity alone does not change this requirement.
The working
16 × 8 × 10 = 1,280 cubic inches. Divide by 231 = 5.54 US gal. Multiply by 3.78541 = 20.98 L.
| Fill assumption | US gal | Litres |
|---|---|---|
| 80% of geometric | 4.43 | 16.78 |
| 85% of geometric | 4.71 | 17.83 |
| 90% of geometric | 4.99 | 18.88 |
| 100% of geometric | 5.54 | 20.98 |
Adjust measurements with the tank volume calculator
Questions before you buy
What dimensions does this 5.5 gallon calculation use?
It uses a rounded 16 × 8 × 10 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the tank volume estimate for a 5.5 gallon tank?
5.54 US gallons · 20.98 litres
Equipment to check
Compare aquarium measuring tape. Check dimensions, capacity and product instructions before buying.
As an Amazon Associate I earn from qualifying purchases.