Building a Backyard Fish Pond
If you are planning to upgrade the look of your garden, adding a fish pond or a garden pond to your backyard can be one of your best options. With an artificial pond, you can plant aquatic plants, keep fish, and create a relaxing water feature. Our Pond Calculator helps you plan every aspect of your pond — from sizing to lining and water filling costs.
How to Use Our Pond Calculator
Using our pond calculator is straightforward. Follow these steps:
- Choose your unit system — Imperial (feet, gallons) or Metric (meters, liters).
- Select the shape that best resembles your pond: Rectangular, Circular, or Oval.
- Enter the maximum dimensions of your pond (length, width, and depth — or diameter for circular ponds). The calculator will instantly show you the pond surface area and the total water volume it can hold.
- Enter the liner overlap — the extra width on each side that folds up the bank. A typical overlap is 2 ft (0.6 m). The calculator will then display the liner dimensions and area you need.
- Optionally open the "Liner cost" and "Water cost" sections to estimate project expenses. Enter your local price per square foot (or m²) for the liner, and price per gallon (or liter) for water. Choose your preferred currency — including USD, RUB, EUR, GBP, and 16 other world currencies.
How Do I Calculate Pond Volume?
Pond volume depends on the shape:
- Rectangular pond: Volume = Length × Width × Depth. In Imperial: cubic feet × 7.48 = US gallons.
- Circular pond: Volume = π × (Diameter ÷ 2)² × Depth.
- Oval pond: Volume = π × (Length ÷ 2) × (Width ÷ 2) × Depth.
Knowing your pond volume is essential for calculating the correct amount of dechlorinator, pond salt, or fish medication, and for choosing the right pump and filtration system.
How Do I Calculate How Much Pond Liner I Need?
The liner must cover the bottom and all sides of the pond, plus an overlap around the top edge to anchor it in place. The formulas are:
- Liner Length = Pond Length + (2 × Depth) + (2 × Overlap)
- Liner Width = Pond Width + (2 × Depth) + (2 × Overlap)
- For a circular pond, you need a square sheet: Side = Diameter + (2 × Depth) + (2 × Overlap)
A standard overlap of 2 ft (60 cm) on each side is recommended. This allows the liner to be secured under rocks or edging stones.
How to Install a Pond Liner
Proper liner installation is key to a long-lasting, clear pond:
- Excavate to 3 inches (8 cm) deeper than your intended depth to accommodate the underlayment thickness.
- Remove all sharp rocks and roots from the bottom and walls to prevent punctures.
- Lay the pond liner underlay (geotextile fabric) over the excavated area. This cushions the liner and protects it from sharp objects.
- Lay the pond liner on top of the underlay. Smooth out as many wrinkles as possible from the center outward. Let the liner warm in the sun for easier handling.
- Begin filling with water slowly. As the water weighs down the liner, fold and tuck any remaining creases.
- Trim the liner, leaving a 12–18 inch (30–45 cm) overlap around the edge. Secure it under edging stones, rocks, or a trench.
Plastic vs. Rubber Pond Liner
EPDM rubber liners are the most popular choice for garden ponds. They are flexible, durable, and typically last 20–30 years. PVC (plastic) liners are less expensive but become brittle over time when exposed to UV light. For fish ponds, always choose a fish-safe liner (free of toxic plasticizers).
FAQs
- How deep should a fish pond be?
- At least 2 feet (60 cm). For koi or goldfish that overwinter outdoors, 3–4 feet (90–120 cm) is recommended so fish can survive below the ice layer.
- How many gallons is my pond?
- Use our pond volume calculator above. Enter your pond dimensions and choose your unit system. The result is shown in both gallons and cubic feet (or liters and cubic meters).
- What size pond liner do I need?
- Use the liner section of our calculator. Enter your pond dimensions and liner overlap (typically 2 ft / 0.6 m) to get the exact liner sheet size you need to purchase.
- Can I use the same liner size for underlayment?
- Yes. The underlayment (geotextile fabric) should be the same dimensions as the liner, so use the same liner dimensions calculated above.