Setup & Sizing
Pond Volume Calculator
Work out the water volume of a rectangular, round or kidney-shaped pond. Enter average length, width and depth in metres or feet and we'll return litres, UK gallons and US gallons.
Pond Volume Calculator
For irregular depth, average the shallow and deep sections.
Water volume
4,800L
- UK gallons
- 1,056
- US gallons
- 1,268
- Cubic metres
- 4.8 m3
How pond volume is worked out
A rectangular pond is simply length x width x depth. A round or oval pond uses the ellipse area formula: pi x (length / 2) x (width / 2) x depth. For kidney or irregular shapes we use the standard 0.8 multiplier against the rectangular bounding box, which most UK pond suppliers and the RHS use as a first-pass estimate.
Formulas:
- Rectangular:
L x W x D x 1000= litres (metres) - Round / oval:
pi x (L/2) x (W/2) x D x 1000= litres - Kidney / irregular:
0.8 x L x W x D x 1000= litres
Why average dimensions?
Ponds are rarely uniform - the shallows are often 30-40 cm and the deep section 80-100 cm. Use the average depth for the input, not the deepest point. The same goes for length and width on a kidney-shaped pond: measure at the widest and narrowest and take the middle.
Treatment & stocking caveats
For medication dosing, start with 90% of the calculated volume - rocks, plants and waste reduce the true water volume. For stocking, remember that koi grow to 60-80 cm as adults and each needs 250 litres+ of their own space. When in doubt, go bigger on filtration and smaller on stocking.
Frequently asked questions
Why calculate the volume of my pond?
Pond volume is the number every other pond decision hangs off. It tells you how big a pump and UV clarifier you need, how much treatment to add, and how many fish the pond can safely hold. Over-dosing a pond can kill fish quickly; under-dosing lets parasites or algae take hold.
How accurate is this for an irregular pond?
For kidney and irregular shapes we use the standard 0.8 rectangular-bounding-box approximation, which is accurate to within 5-10% for most garden ponds. If your pond has very deep or very shallow sections, break it up into two or three imaginary rectangles, calculate each and add them together.
What size pump do I need for my pond?
The usual UK guideline is to turn the whole pond over at least once an hour. So for a 4,000 litre pond, pick a pump rated at 4,000+ litres per hour at the actual head height it has to pump to. Our flow-rate calculator helps you adjust for head loss and canister mulm.
How many fish can my pond hold?
For coldwater fish like goldfish and shubunkins, the safe stocking level is roughly one inch of fish per 4.5 litres (1 inch per gallon). For koi, plan on 250-500 litres per adult fish minimum because they grow large and are heavy waste producers.
Related calculators
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Work out the right pond liner size from pond length, width and depth with a 30 cm safety overlap built in.
Flow Rate
Find the filter turnover (litres per hour) you should be aiming for based on tank volume and stocking style.
Dosing
Scale any liquid aquarium product (ferts, dechlorinator, treatments) to your exact tank volume.