How many gallons does a 45 gallon tank hold?
36 × 12 × 24 in · freshwater planning
45 gallon · tank volume
The working
36 × 12 × 24 = 10,368 cubic inches. Divide by 231 = 44.88 US gal. Multiply by 3.78541 = 169.9 L.
| Fill assumption | US gal | Litres |
|---|---|---|
| 80% of geometric | 35.91 | 135.92 |
| 85% of geometric | 38.15 | 144.42 |
| 90% of geometric | 40.39 | 152.91 |
| 100% of geometric | 44.88 | 169.9 |
First decisions for this medium setup
For this medium rectangle, work from the base upward: every inch of height represents 1.87 gallons. Marking a waterline makes repeat fills more consistent. A tall rock or a wood arrangement displaces an unknown amount; a running total from measured containers is more useful than assigning decor a guessed percentage.
45 gallon equipment and layout plan
This upright rectangle adds vertical room without a wider bottom. The 36 × 12-inch base has an aspect ratio of 3:1. A lid or light must span roughly 36 inches; measure rim openings and bracket adjustment before ordering.
| Volume interpretation | US gallons |
|---|---|
| Marketed nominal size | 45 |
| Rounded rectangle, before glass | 44.88 |
| Inside panes, brim full model | 41.97 |
| Inside panes, 1 inch below rim | 40.21 |
| 2-inch bed envelope, before decor | 3.74 |
For the inside-pane comparison, 35.5 inches of length times 11.5 of width times 23.75 of height gives 41.97 gallons. This assumes 0.25-inch glass and a brim-full fill. Leave room for the real waterline; decor displacement requires measurement, and water remains between substrate grains.
Moving up from the 40 gallon long changes geometric gallons before glass from 39.9 to 44.88: an increase of 12.5%. Budget for the larger requirement rather than reusing the smaller plan unchanged.
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.
Adjust measurements with the tank volume calculator
Questions before you buy
What dimensions does this 45 gallon calculation use?
It uses a rounded 36 × 12 × 24 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the tank volume estimate for a 45 gallon tank?
44.88 US gallons · 169.9 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.