How many gallons does a 29 gallon tank hold?
30 × 12 × 18 in · freshwater planning
29 gallon · tank volume
29 gallon equipment and layout plan
A rectangular layout supports a straight front swimming lane and a rear equipment zone. The 30 × 12-inch base has an aspect ratio of 2.5:1. A lid or light must span roughly 30 inches; measure rim openings and bracket adjustment before ordering.
| Volume interpretation | US gallons |
|---|---|
| Marketed nominal size | 29 |
| Rounded rectangle, before glass | 28.05 |
| Inside panes, brim full model | 26.07 |
| Inside panes, 1 inch below rim | 24.6 |
| 2-inch bed envelope, before decor | 3.12 |
The marketed 29 gallons and calculated 28.05 gallons describe different things. Subtract twice the 0.25-inch pane thickness from length and width, but only the bottom pane from height. The resulting inside dimensions are 29.5 × 11.5 × 17.75 inches. Rounded external dimensions and framing limit precision.
Moving up from the 25 gallon changes geometric gallons before glass from 24.94 to 28.05: an increase of 12.5%. Budget for the larger requirement rather than reusing the smaller plan unchanged.
First decisions for this small setup
The 29-gallon name is a buying category. For fitting equipment, record all three measurements: 30 inches along the front, 12 front to back, and 18 vertically. Two similarly named tanks can have different floors. Compare inside dimensions before copying another setup’s fill amount.
The working
30 × 12 × 18 = 6,480 cubic inches. Divide by 231 = 28.05 US gal. Multiply by 3.78541 = 106.19 L.
| Fill assumption | US gal | Litres |
|---|---|---|
| 80% of geometric | 22.44 | 84.95 |
| 85% of geometric | 23.84 | 90.26 |
| 90% of geometric | 25.25 | 95.57 |
| 100% of geometric | 28.05 | 106.19 |
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 29 gallon calculation use?
It uses a rounded 30 × 12 × 18 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the tank volume estimate for a 29 gallon tank?
28.05 US gallons · 106.19 litres
Equipment to check
Compare aquarium measuring tape. Check dimensions, capacity and product instructions before buying.
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