Pond Size Reference
Pond volume lined up against safe stocking for goldfish and koi, the filter turnover each needs, and typical water-change volumes — plus a feeding-by-temperature table below. Every figure here is computed live by the same functions behind the Pond Volume, Fish Stocking, Filter Turnover, Water Change, and Feeding Amountcalculators — not a separate, hand-typed table.
Pond volume → stocking, turnover, and water change
| Example pond | Gallons | Goldfish max (in) | Koi max (in) | Goldfish turnover (GPH) | Koi turnover (GPH) | 10% change (gal) | 20% change (gal) |
|---|---|---|---|---|---|---|---|
| Small (e.g. 6 x 4 ft, 2 ft deep) | 359.06 | 35.9 | 18 | 179.53 | 359.06 | 35.91 | 71.81 |
| Medium (e.g. 10 x 6 ft, 2.5 ft deep) | 1,122.08 | 112.2 | 56.1 | 561.04 | 1,122.08 | 112.21 | 224.42 |
| Large (e.g. 15 x 10 ft, 3 ft deep) | 3,366.23 | 336.6 | 168.3 | 1,683.12 | 3,366.23 | 336.62 | 673.25 |
| Very large / koi-scale (e.g. 20 x 15 ft, 3.5 ft deep) | 7,854.55 | 785.5 | 392.7 | 3,927.28 | 7,854.55 | 785.46 | 1,570.91 |
| Show-koi scale (e.g. 30 x 20 ft, 4 ft deep) | 17,953.25 | 1795.3 | 897.7 | 8,976.63 | 17,953.25 | 1,795.33 | 3,590.65 |
“Max” stocking figures are the guideline ceiling for that fish type alone (all goldfish, or all koi) at zero current stock — not a recommended target, and not a figure that adds together across both fish types for a mixed pond. Gallons for each example pond come from a simple rectangular shape at the stated dimensions; an oval, round, or irregular pond of similar size will land on a different, usually lower, gallons figure for the same footprint.
Feeding by water temperature
| Water temperature | Feeding rate | Daily ration (oz) | Per feeding (oz) |
|---|---|---|---|
| Below 50°F (dormant) | 0% body weight/day | 0 | 0 |
| 50-59°F (light) | 0.5% body weight/day | 0.08 | 0.04 |
| 60-74°F (normal) | 1% body weight/day | 0.16 | 0.08 |
| 75°F and above (active) | 2% body weight/day | 0.32 | 0.16 |
Figures shown are for an illustrative 16-ounce (1 lb) combined fish weight, split across 2 feedings per day — the same defaults the Feeding Amount Calculator uses. Scale the ounces proportionally to your own fish's actual combined weight, or enter your exact weight directly into the calculator for an exact figure.
How these numbers are derived
Every gallons figure in the first table comes from calling the same pond volume function the Pond Volume Calculatoruses, against a stated example shape and set of dimensions for that size class — nothing here is typed in as a round number. From that gallons figure, the stocking, turnover, and water-change columns are each computed by calling the fish stocking, filter turnover, and water change functions directly, exactly as if you'd entered that gallons figure into each calculator yourself.
That's why the koi columns move in lockstep with the goldfish columns at a fixed ratio: koi stocking capacity is always half the goldfish figure at the same volume (20 gallons per inch versus 10), and koi turnover is always double the goldfish figure (a 1-hour turnover target versus 2 hours). Those relationships aren't coincidences built into this table — they're the direct, unavoidable consequence of the same defaults the calculators apply, which is exactly the point of deriving this reference from the calculators rather than writing a parallel table that could quietly drift out of step with them.
The feeding table below uses a different starting input — total fish weight and water temperature, not pond volume — which is why it's shown as its own small table rather than an extra column on the pond-size table above. It steps through the same four temperature bands the Feeding Amount Calculator uses, for one illustrative fish weight, so the shape of the curve (zero when dormant, doubling at each warmer band) is visible at a glance.
Frequently Asked Questions
Where do the gallons figures in the table come from?
Each row starts from an example pond shape and dimensions (all simple rectangles here, for a clean side-by-side comparison), run through the same calculatePondVolume() function behind the Pond Volume Calculator. The gallons figure isn't typed in directly — it's computed, so it always matches what the calculator itself would report for those dimensions.
Why is the koi turnover figure always exactly double the goldfish figure?
Filter turnover targets are tied to fish type: koi are sized for a 1-hour turnover and goldfish for a 2-hour turnover on the same volume of water, and since turnover time and required flow are inversely related, halving the turnover time exactly doubles the required GPH. That's a direct consequence of the calculator's defaults, not a coincidence specific to these example ponds.
Why is the koi stocking figure always exactly half the goldfish figure?
The stocking guideline uses 10 gallons per inch of adult goldfish versus 20 gallons per inch of adult koi, since koi are larger-bodied and produce more waste per inch of length. Double the gallons-per-inch requirement means half the guideline capacity in inches, for the same pond volume.
Should I treat these numbers as a guarantee for my own pond?
No. These are planning guidelines, not a precise biological formula — real capacity also depends on filtration strength, aeration, planting, and how carefully a pond is fed and maintained. Use this table to sanity-check where a given pond size roughly lands, then run your own exact dimensions and stocking plans through the individual calculators.
Why is the feeding table shown separately from the pond-size table?
Feeding amount depends on total fish weight and water temperature, not on pond volume directly, so it doesn't fit the same volume-based rows as stocking, turnover, and water-change figures. The feeding table uses one illustrative fish weight across all four temperature bands so you can see the shape of the curve — scale the ounces proportionally to your own fish's actual combined weight, or use the Feeding Amount Calculator directly for an exact figure.
Planning reference only. Treat every figure here as a starting point for comparison, not a guarantee for your specific pond — real capacity also depends on filtration strength, aeration, planting, and how carefully a pond is fed and maintained.
Use it with
- Pond Volume Calculator— get an exact gallons figure for your own pond's actual shape and dimensions.
- Fish Stocking Density Calculator— check your real fish count and type against your exact volume.
- Filter Turnover (GPH) Calculator— get a precise pump flow target, including for a custom turnover time if your pond is stocked above guideline.
- Water Change Calculator— work out exact gallons, litres, and bucket counts for your own routine or emergency change.
- Feeding Amount Calculator— enter your fish's actual combined weight for an exact daily ration at today's water temperature.
- The Nitrogen Cycle: Why a New Pond Must Be Cycled Before You Add Fish — none of the stocking figures above are safe to reach on day one in an uncycled pond.
- Realistic Stocking: Goldfish vs Koi in the Same Size Pond — worked examples of exactly how the goldfish/koi gap above plays out with real fish counts.