How many gallons is my pond?

Multiply length × width × average depth in feet, then by 7.48. A 12 × 8 ft pond averaging 2.5 ft deep is 240 cubic feet, or about 1,795 gallons. For an oval or kidney-shaped pond multiply that by 0.785; for a round pond use 3.14 × radius × radius × depth × 7.48.

How do I calculate pond volume in litres?

Measure in metres and multiply length × width × average depth × 1,000. A 3 × 2 m pond averaging 0.6 m deep holds 3.6 cubic metres, which is 3,600 litres.

What size pump do I need for my pond?

For koi, a pump that moves the whole pond volume once an hour at your head height: about 900 gallons per hour for a 900 gallon pond. A lightly stocked pond needs at least half that, once every two hours. A waterfall needs about 1,500 gallons per hour per foot of spillway width, so with a waterfall use whichever figure is larger.

Should I use the maximum or the average depth?

Average depth for volume, maximum depth for the liner. Shelves and sloped sides mean a pond holds less than its deepest point suggests, so the average gives the realistic volume to dose and size a pump from.

How do I measure the volume of an irregular pond?

Pick the oval shape and enter the longest length and the widest width. That treats the pond as an ellipse, which is closer to most freeform ponds than a rectangle. For an L-shaped or two-part pond, work out each part separately and add them.

Pond Volume Calculator: Gallons, Litres & Pump Size

JavaScript is disabled in your browser, so the interactive calculator below won't run. The math, formula, and worked example are all written out further down this page under “How this is calculated.” Enable JS (or open this page in another browser) to use the live calculator.

Whether you compute by hand or in the calculator, the same caveat applies: verify against your test kit and the linked primary source before dosing. reefcalcs is reference information, not veterinary or engineering advice.

Pond volume and pump flow

Pond shape

For a kidney or freeform pond, pick oval and use the longest length and widest width.

Length (ft)

Width (ft)

Average depth (ft)

Measure the depth at several points and average them. Shelves and sloped sides make the average less than the deepest point.

Waterfall width (ft, optional)

The width of the spillway lip only, not the frame rocks.

Pond volume

898US gal

747 UK gal

Litres

3,398L

3.4 m³

Pump for a koi pond

898gal/h

3,398 L/h: the whole pond once an hour

Pump for a lightly stocked pond

449gal/h

1,699 L/h: once every two hours

Choose the pump by the flow it delivers at your head height (the height from the pond surface to the top of the waterfall or filter inlet), read from the pump's own flow chart. Pumps deliver less the higher they lift, and long or narrow pipe runs cost more. If you have a waterfall, use whichever of the turnover and waterfall figures is larger.

Sponsor this calculator

What you'll need for this

Affiliate links. As an Amazon Associate, reefcalcs earns from qualifying purchases, at no extra cost to you.

Submersible pond pump

Pick one that still delivers your flow at your head height, from its flow chart.

See options on Amazon

How this is calculated

Volume (feet in, US gallons out)
  rectangle  L × W × average depth × 7.48
  oval       L × W × average depth × 7.48 × π/4   (π/4 ≈ 0.785)
  circle     π × (diameter ÷ 2)² × average depth × 7.48
  7.48 = US gallons per cubic foot (1,728 in³ ÷ 231 in³)
Volume (metres in)
  L × W × average depth × 1,000 = litres

Pump flow (gallons per hour)
  koi pond          pond gallons × 1   (once an hour)
  lightly stocked   pond gallons ÷ 2   (once every two hours)
  waterfall         1,500 × spillway width in feet
  use the larger of turnover and waterfall,
  delivered at your head height

Aquascape gives the rectangular formula as "Length x Width x Average Depth x 7.48 = Approximate Gallons", and the metric one as "x 1000 = Approximate Liters". The oval and circle versions are the same calculation with the area of an ellipse or circle in place of length × width.

Why average depth matters

Most garden ponds have shelves for plants and sloped sides, so they hold less water than a box of the same length, width and maximum depth. Measure the depth at several points across the pond and average them. If you can, check the result the first time you fill: a water meter, or the time a hose takes to fill a bucket, gives you a real figure to dose from.

Sizing the pump

Cotswold Koi's guidance is that the water "should circulate once per hour" in a koi pond, and that lightly stocked ponds should be circulated "at least once every two hours". A waterfall sets its own minimum: Aquascape uses 1,500 gallons per hour for each foot of spillway width on a residential waterfall. Pumps are rated at zero lift, and "the higher the water is pumped vertically the lower the pump's flow rate", so pick a pump that still delivers the flow you need at your head height, from its own flow chart. For the liner, use the pond liner calculator, which works from the maximum depth instead.

FAQ

How many gallons is my pond?: Multiply length × width × average depth in feet, then by 7.48. A 12 × 8 ft pond averaging 2.5 ft deep is 240 cubic feet, or about 1,795 gallons. For an oval or kidney-shaped pond multiply that by 0.785; for a round pond use 3.14 × radius × radius × depth × 7.48.
How do I calculate pond volume in litres?: Measure in metres and multiply length × width × average depth × 1,000. A 3 × 2 m pond averaging 0.6 m deep holds 3.6 cubic metres, which is 3,600 litres.
What size pump do I need for my pond?: For koi, a pump that moves the whole pond volume once an hour at your head height: about 900 gallons per hour for a 900 gallon pond. A lightly stocked pond needs at least half that, once every two hours. A waterfall needs about 1,500 gallons per hour per foot of spillway width, so with a waterfall use whichever figure is larger.
Should I use the maximum or the average depth?: Average depth for volume, maximum depth for the liner. Shelves and sloped sides mean a pond holds less than its deepest point suggests, so the average gives the realistic volume to dose and size a pump from.
How do I measure the volume of an irregular pond?: Pick the oval shape and enter the longest length and the widest width. That treats the pond as an ellipse, which is closer to most freeform ponds than a rectangle. For an L-shaped or two-part pond, work out each part separately and add them.

Share / embed this calculator

Paste this snippet into any blog or forum post that allows raw HTML to embed the calculator.

<iframe
  src="https://reefcalcs.com/embed/pond-volume/"
  width="100%"
  height="720"
  style="border: 2px solid #111412; max-width: 720px;"
  loading="lazy"
  title="reefcalcs Pond Volume Calculator"
></iframe>

Sources & references

1.
Aquascape — Water volume in a rectangular pond
https://support.aquascapeinc.com/hc/en-us/articles/48507090702612-Water-Volume-in-a-Rectangular-Pond
2.
Aquascape — What flow rate is needed for a waterfall
https://support.aquascapeinc.com/hc/en-us/articles/48506913796244-Waterfall-What-flow-rate-is-needed-for-a-waterfall
3.
Cotswold Koi — What size pond pump do I need for my koi pond?
https://www.cotswoldkoi.co.uk/knowledge-centre/what-size-pond-pump-do-i-need-for-my-koi-pond/
4.
NIST — 1 US gallon = 231 cubic inches
https://www.nist.gov/pml/owm/si-units-volume

Last reviewed 2026-10-29