Pond Size Calculator

Estimate pond volume, liner size and a recommended pump flow using simple length, width and average depth inputs. Useful for backyard ponds, koi ponds and small reservoirs.

Length

Width

Average Depth

Pond Shape Rectangle / Square Oval / Ellipse Circular

Units Meters (m) Feet (ft)

Desired turnover per hour 1× per hour (general) 2× per hour (koi pond) 3× per hour (heavy filtration)

Calculate Pond Size Reset

Result:

Enter dimensions and click Calculate Pond Size.

Formulas & Notes

Volume for rectangle: V = L × W × D. For oval (ellipse): V = π/4 × L × W × D. For circle: use diameter = length, V = π/4 × D² × Depth. Convert m³ → litres (×1000) and m³ → US gallons (×264.172) or imperial gallons (×219.969).

Measurements You Need

To use a pond size calculator effectively, you’ll need three basic numbers:

• Length – the longest point of your pond
• Width – the widest point
• Average Depth – not the deepest point, but the middle-ground depth

Ponds rarely have perfect shapes, so average measurements give a realistic estimate.

Formula Used for Pond Volume

Most calculators use a simple formula to convert measurements into gallons or litres:

Volume (Gallons) = Length × Width × Average Depth × 7.48
Volume (Litres) = Length × Width × Average Depth × 28.31

Why Accurate Pond Size Matters

Getting the right pond volume helps in several important areas:

1. Pump and Filter Selection

Pond equipment is rated by gallons or litres per hour. If you know the exact water volume, you can choose a pump that circulates the entire pond at least once per hour and select a filter strong enough to maintain water clarity.

2. Liner and Underlayment Calculations

Using the correct dimensions lets you determine the exact size of pond liner you need. This prevents underestimating (which can cause leakage) or overestimating (which increases costs).

3. Fish Capacity and Water Quality

If you plan to keep fish, knowing the pond’s capacity helps you avoid overcrowding. Overstocking reduces oxygen levels and increases maintenance. A properly calculated pond size keeps fish healthier and reduces algae growth.

4. Chemical Treatment Accuracy

Water treatments, such as dechlorinators or algaecides, require exact dosing based on total pond volume. The calculator ensures you use the right amount to keep the pond safe and balanced.

Final Thoughts

A pond size calculator is essential for designing and maintaining a healthy, well-functioning pond. With just a few basic measurements, you get accurate volume estimates that guide equipment selection, maintenance and long-term water quality.