Pond Calculator

Estimate your pond's water volume, liner size, and pump requirements all in one place. Supports multiple pond shapes and provides useful metrics like fish capacity, acre-feet, and cost to fill.

Average pond depth, not just deepest point

Adjusts for non-rectangular shapes

Extra liner material extending beyond pond edges

Optional: Check your local water bill

Volume (gal) = Surface Area × Avg Depth × 7.48052

Rectangular Surface Area = L × W
Circular Surface Area = π × r²
Oval Surface Area = π × (L/2) × (W/2)

Liner Size: L + 2D + 2O × W + 2D + 2O
(D = depth, O = overlap)

Pump Flow = Volume (gal) × 0.5 to 1.0 per hour
A 10×8 ft rectangular pond, 3 ft average depth: Surface = 80 sq ft. Volume = 80 × 3 × 7.48 = 1795 gallons. Liner = (10+6+4) × (8+6+4) = 20 × 18 = 360 sq ft. Pump: minimum 898 GPH, recommended 1795 GPH. Capacity: ~35 small fish.

How do I calculate how much water my pond holds?

For rectangular ponds: multiply length × width × average depth × 7.48 to get gallons. For circular ponds: use π × radius² × depth × 7.48. For irregular shapes, multiply the rectangular estimate by a shape factor (0.80-0.90). Average depth should account for shallow shelves and deeper areas.

What size pond liner do I need?

Add twice the maximum depth plus 2-3 feet of overlap to both length and width. For a 10×8 ft pond that is 3 ft deep: liner length = 10 + 2×3 + 2×2 = 20 ft, liner width = 8 + 2×3 + 2×2 = 18 ft. Always round up to standard liner sizes for easiest installation.

What pump size do I need for my pond?

Your pump should circulate the entire pond volume at least once per hour. For a 1500-gallon pond, choose a pump rated for 1500 GPH or higher at your waterfall height. If you have fish or heavy plant load, increase to 1.5-2× the volume per hour. Head height reduces pump flow, so check the pump curve.

How many fish can I put in my pond?

A general rule is 1 inch of fish per 10 gallons of water, or roughly one small koi per 50 gallons. For a 1000-gallon pond, that means 20 small fish or 10-15 goldfish. Overstocking stresses fish and requires more filtration. A good biological filter should handle at least the pond's full volume per hour.

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