TryBuildCalcKoi Pond Volume Calculator (Gallons & Pump GPH)
Size your koi pond's volume and pump instantly.
🕒 Last updated: September 23, 2026
Inputs
ℹ️Rectangular and Circular use exact geometric volume; Oval uses the exact ellipse-area formula; Irregular/Kidney uses a disclosed mid-range approximation, since no exact formula exists for a freeform shape.
ℹ️The true AVERAGE depth across the whole basin, not the deepest point — sloped walls mean average depth is genuinely shallower than max depth. Liner sizing separately uses your pond's maximum depth below.
ℹ️The depth at your pond's single DEEPEST point — used only for liner sizing, since the liner has to physically reach the bottom and back up. Must be at least the average depth above (equal for straight, vertical-walled ponds).
Marginal Shelf Zone
A shallow planting ledge around the perimeter, at its own shallower depth — its footprint is subtracted from the main basin, not added on top.
Pond Liner
ℹ️Extra material left at the edge for anchoring/trimming — 2 ft is a commonly-cited standard, adjustable here.
Pump / Filtration
ℹ️Drives both the pump turnover-rate target and which fish-stocking guideline (volume-based or surface-area-based) is shown.
Cost
Water Volume
4,189
US gal (15,857 L, 560 cu ft)
Liner Size Needed
27 x 21
ft (606.7 sq ft to purchase)
Recommended Pump
12,567
GPH rated (min. 8,378 GPH delivered)
Shape: Rectangular / Square — Pond Type: Koi Pond
Pond Geometry
16 x 10 ft
Average depth: 3.5 ft / Maximum depth: 4.5 ft
Surface area: 160 sq ft (14.9 m²)
Water Volume
4,189 US gal (3,488 Imperial gal)
15,857 litres (15.86 m³)
Cubic feet: 560 cu ft (20.74 cu yd)
Liner & Underlayment
Bounding size: 16 x 10 ft, max depth 4.5 ft, overlap 2 ft
Liner cut size: 27 x 21 ft (567 sq ft)
Purchase area (incl. 7% waste): 606.7 sq ft
Underlayment: 606.7 sq ft (same footprint as liner)
Pump / Filtration
Turnover target: 2x/hr (Koi Pond)
Minimum delivered flow: 8,378 GPH
Recommended rated pump: 12,567 GPH
Fish Stocking Guideline
Roughly 160 in of fish (surface-area-based). Roughly 1 sq ft of water surface per inch of koi — koi need surface oxygen exchange more than raw volume.
⚠ General planning guideline only — filtration, aeration, and fish's eventual mature size also affect real safe stocking.
Assumptions Used
Rectangular / Square pond, average water depth (not maximum depth). Volume uses an exact geometric formula for this shape. No marginal shelf is included. Liner sized using bounding length/width, the pond's maximum depth (not average), and a 2 ft overlap allowance, plus a 7% purchase waste allowance; underlayment reuses the same purchase area. Pump sized from a 2x/hr turnover target for Koi Pond, with a recommended rated spec at 1.5x the minimum delivered flow to account for head-height/pipe-friction losses. This calculator computes volume, liner, and pump-sizing estimates only — it does not verify excavation, structural, electrical, or local permitting requirements.
Approximate results for planning only. Verify with a professional.
Diagram simplified for clarity (not to scale) — depth bands reflect relative depth, not exact scale.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Pond/Water-Feature Volume Calculator.
Koi ponds need more turnover and deeper water than goldfish ponds
Koi are heavy waste producers and grow much larger than goldfish, so this calculator applies a higher 2.0x-per-hour turnover rate when Koi Pond is selected — meaningfully more active filtration than a goldfish pond's 1.0-1.5x/hr range. Koi also need a deeper pond (commonly 3+ ft) for both temperature stability and predator protection.
This page defaults to a 16 x 10 ft pond at 3.5 ft average depth with the Koi Pond preset selected — edit the inputs above to match your own pond's size and depth.
Pond Calculator Formula: How Is It Determined?
Your pond's shape, dimensions, and average depth combine into a volume figure, which then drives liner sizing, pump GPH, and a fish-stocking guideline.
Step 1 — Volume by Shape
Rectangular/Square: Volume = Length x Width x Average Depth
Circular: Volume = pi x (Diameter/2)^2 x Average Depth
Oval/Elliptical: Volume = (pi/4) x Length x Width x Average Depth
Irregular/Kidney: Volume = Length x Width x Average Depth x 0.75 (disclosed mid-range estimate)
Rectangular, Circular, and Oval use exact geometric formulas; Irregular/Kidney uses a disclosed approximation since a freeform outline has no exact formula — break a highly irregular pond into rectangular sub-sections and sum them for a more accurate figure.
Step 2 — Marginal Shelf Zone (optional)
Main Basin Footprint = Footprint of the same shape, shrunk by (2 x Shelf Width)
e.g. Rectangular: (Length − 2 x Shelf Width) x (Width − 2 x Shelf Width)
e.g. Circular: pi x ((Diameter/2) − Shelf Width)^2
Shelf Footprint = Total Footprint − Main Basin Footprint
Total Volume = (Main Basin Footprint x Main Depth) + (Shelf Footprint x Shelf Depth)
The shelf's footprint is subtracted from the main basin — it occupies space that would otherwise be full-depth basin, not additional pond area. The shelf band is measured as the pond's own footprint minus the shrunk inner basin, rather than simply perimeter x shelf width, because that shortcut double-counts the corners where the band meets itself (a 12 x 8 ft pond with a 1 ft shelf is 36 sq ft of shelf, not the 40 sq ft the perimeter shortcut gives).
Step 3 — Liner Size
Liner Length = Bounding Length + (2 x Maximum Depth) + Overlap Allowance
Liner Width = Bounding Width + (2 x Maximum Depth) + Overlap Allowance
Uses the pond's MAXIMUM depth (deepest point, main basin or shelf), not average depth — the liner has to physically reach down and back up. A small purchase waste allowance is added on top; underlayment reuses the same purchase area.
Step 4 — Pump GPH
Minimum GPH = Volume (gal) x Turnover Rate (0.5x-2.0x/hr by pond type)
Recommended Rated GPH = Minimum GPH x 1.5
Waterfall (optional): + Spillway Width (in) x GPH per inch (100 light / 200 heavy)
Turnover rate scales with stocking level; the 1.5x factor accounts for head-height/pipe-friction losses between a pump's printed rating and its real delivered flow. A waterfall adds its own GPH on top, reported as a separate line item.
Step 5 — Fish Stocking Guideline
Goldfish/general (volume-based): Max Fish Inches = Volume (gal) / 10
Koi (surface-based): Max Fish Inches = Surface Area (sq ft) / 1
A general planning guideline only — only the rule matching your selected pond type is shown.
Step 6 — Cost
Line Cost = Purchase Quantity (sq ft/estimate) x Unit Price
Total = Liner + Underlayment + Pump
Every cost line is priced off the actual purchase quantity, and every cost field is zero unless cost estimation is enabled.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value |
|---|---|
| Pond Size | 16 x 10 ft, avg depth 3.5 ft, max depth 4.5 ft |
| Shape | Rectangular / Square |
| Pond Type | Koi Pond |
Step 1 — Volume
| Calculation | Result |
|---|---|
| 160 sq ft surface x depth | 560 cu ft (4189 US gal) |
Step 3 — Liner Size
| Calculation | Result |
|---|---|
| 16 + (2 x 4.5) + 2 ft overlap | 27 x 21 ft (606.7 sq ft to buy) |
Step 4 — Pump GPH
| Calculation | Result |
|---|---|
| 4189 gal x 2x/hr | 8378 GPH min (12567 GPH recommended) |
Figures above are rounded for display; the real quantities are always calculated from full, unrounded values.
Therefore, a 160 sq ft rectangular pond at 3.5 ft average depth holds 4189 US gal (15857 L), needs a 27 x 21 ft liner, and a pump rated at least 12,567 GPH.