How pond volume is calculated
For a roughly rectangular pond, gallons = length × width × average depth (all in feet) × 7.48, because one cubic foot holds 7.48 US gallons. A 10 × 6 ft pond averaging 3 ft deep holds 180 × 7.48 ≈ 1,346 gallons. Use the average depth, not the deepest point.
Working in metres? Multiply cubic metres by 264.2 to get US gallons. For a circular pond use π × radius² × average depth × 7.48 — an 8 ft wide round pond averaging 2 ft deep holds about 50.3 × 2 × 7.48 ≈ 752 gallons.
The same numbers feed straight into the gallons to liters calculator.
Why volume matters for fish
Knowing gallons lets you size pumps, filters and stock levels, and dose treatments correctly. A common koi guideline is hundreds of gallons per fish. For an indoor tank instead, use the aquarium volume calculator.
A good rule of thumb is that the pump should turn over the whole volume at least once an hour, so the 1,346-gallon example wants a pump rated near 1,350 gallons per hour. Rocks, planting shelves and a gravel base typically remove 5–10% of the theoretical volume, so round down before calculating any treatment dose.
Once that is settled, the cubic feet calculator takes care of the next part.
How to use this calculator
Enter the pond length, width and average depth in feet to get the total gallons. Building it up with soil first? See the soil calculator.
Take depth readings at several points with a marked stick and average them instead of measuring only the deepest spot. Steep-sided ponds land much closer to the calculated figure than gently sloping ones.
Frequently asked questions
- How many gallons is a 10x6x3 ft pond?
- About 1,346 gallons, using length × width × average depth × 7.48.
- Why multiply by 7.48?
- One cubic foot of water equals 7.48 US gallons, so it converts cubic feet to gallons.
- Should I use average or maximum depth?
- Use average depth. Most ponds are shallower at the edges, so the maximum overstates volume.
- How do I handle an irregular shape?
- Estimate an average length and width, or split the pond into rectangles and add the volumes.
- How accurate is this for a pond with sloping sides?
- Ponds with sloping sides hold noticeably less than the rectangle formula suggests, often 10–20% less. Average several depth readings, or treat the figure as an upper bound when dosing treatments.