What can live in a 38 gallon tank?
36 × 12 × 20 in · freshwater planning
38 gallon · stocking guide
The working
The footprint is 36 × 12 = 432 in². For comparison only, dividing by 30, 45 or 60 in² per adult fish-inch gives the budgets below. Divide by a researched adult size to compare loads; do not treat the result as permission to buy that many fish.
| Comparison category | Area per adult inch | Total adult inches (model only) |
|---|---|---|
| Light | 30 in² | 14.4 |
| Moderate | 45 in² | 9.6 |
| Heavy | 60 in² | 7.2 |
First decisions for this medium setup
Use the 12-inch width to think about shared territory. Bottom fish need connected usable substrate, while schooling fish need open midwater. A tall pile of wood can divide those spaces. Check whether the proposed groups prefer compatible temperatures and water chemistry before combining their separate care sheets.
38 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.
A small tetra school and a separately researched cory group can be a starting layout. Put taller hardscape behind the swimming lane and leave connected open substrate for bottom fish.
| Space check | Available rectangle |
|---|---|
| Horizontal run | 36 in |
| Turning width | 12 in |
| Total base | 432 in² |
| Illustrative 25% hardscape footprint | 108 in² |
| Remaining base in that layout | 324 in² |
The 20-inch height does not extend the 36-inch swimming run. A layout using a quarter of the base for rocks leaves 324 in² before plants and equipment; this is a space illustration, not a fish-count formula. Match adult size, temperature, water chemistry and group behavior before choosing species.
Moving up from the 37 gallon changes square inches of base from 360 to 432: an increase of 20%. Budget for the larger requirement rather than reusing the smaller plan unchanged.
Assumptions and limits
There is no universal inch-per-gallon stocking law. This surface-area model is an editorial comparison aid, not a validated carrying-capacity formula. Filtration, adult size, activity, temperament, swimming length, oxygen and water changes can each rule out a plan. Cycle the tank and test ammonia and nitrite; both should stay at zero before adding fish.
Example plan: A school of 10–12 small tetras with a researched group of 6 suitable corys is a starting plan. Medium species need a separate adult-size and temperament check. Avoid oscars and other large cichlids in this footprint.
Adjust measurements with the stocking guide calculator
Questions before you buy
What dimensions does this 38 gallon calculation use?
It uses a rounded 36 × 12 × 20 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the stocking guide estimate for a 38 gallon tank?
432 in² surface · 36-inch swimming length
Equipment to check
Compare aquarium water test kit. Check dimensions, capacity and product instructions before buying.
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