How do you calculate koi pond volume?

For rectangular ponds: length × width × average depth × 7.48 = gallons. For circular ponds: radius² × π × depth × 7.48. For oval ponds: half-length × half-width × π × depth × 7.48. For irregular or kidney-shaped ponds: length × width × average depth × a shape factor (0.7–0.85) × 7.48. If your pond has varying depths, calculate each depth zone separately and add the results.

How many gallons per koi fish?

A conservative guideline is 250 gallons per adult koi, assuming adequate filtration. Koi grow to 18–24+ inches over their lifespan. Stock based on the adult size your fish will reach, not their current size. A 3,000-gallon pond can comfortably support approximately 10–12 adult koi with proper filtration.

Pond Volume Calculator

Supports multiple depth zones Worker-Powered

Accurate pond volume is the foundation for every other calculation in koi keeping — stocking density, dosing, salt treatment, pump sizing, and filter capacity all depend on knowing your volume. This calculator supports rectangular, circular, oval, and kidney-shaped ponds with multiple depth zones for accurate results.

Enter Your Pond Dimensions

Pond Shape

Measurement Unit

Zone 1 (or entire pond)

Length

Width

Depth (average)

How to Measure Your Pond

Rectangular Ponds

Measure the length and width at the waterline. For depth, measure at the deepest point. If your pond has a consistent depth, use a single zone. If it has a shelf area at one depth and a deeper main area, use two zones — one for the shelf dimensions and one for the deep section.

Circular Ponds

Measure the diameter at the waterline. For depth, measure at the center. If the bottom slopes gradually to a central drain, use the average depth (approximately 2/3 of the maximum depth for a cone-shaped bottom).

Oval Ponds

Measure the longest dimension (length) and the widest dimension (width) at the waterline. The calculator uses the ellipse formula (π × half-length × half-width × depth).

Kidney and Irregular Ponds

For irregular shapes, measure the maximum length and maximum width, then apply a shape factor. A mild kidney shape uses 0.80–0.85. A pronounced kidney with significant narrowing uses 0.70–0.75. A highly irregular shape (L-shaped, multi-lobed) may need 0.65–0.70. When in doubt, use 0.75 and know your actual volume is within ±10%.

Why Accurate Volume Matters

Pond volume is the denominator in every dosing calculation. Salt therapy at 3 ppt in a pond you thought was 2,000 gallons but is actually 3,500 gallons means you only achieved 1.7 ppt — potentially ineffective against the parasite you're treating. Conversely, overestimating volume means overdosing, which can stress or harm fish.

Take the time to measure carefully, and consider breaking your pond into multiple depth zones for a more accurate result.

Related Resources

Stocking Density Calculator — how many koi your pond can support
Salt Dosage Calculator — how much salt for your pond volume
Filter Sizing Calculator — filtration requirements based on volume and fish load
Pump Sizing Calculator — GPH needed for adequate turnover