Advanced options
Volume drives everything: pump and filter sizing, treatment doses and stocking levels. Koi keepers turn water over every 1-2 hours; wildlife ponds without fish need no pump at all. Liner size = (length + 2x depth + 0.6m overlap) x (width + 2x depth + 0.6m).
What The Pond Volume Calculator Works Out
- Pond volume: length x width x average depth x 1,000 for litres, scaled by 0.85 for oval or irregular shapes and 0.785 (pi over four) for circles. A 3 x 2m pond averaging 60cm deep holds 3,600 litres, about 790 gallons. Average depth is the honest input, since most ponds shelve; using the deepest spot overstates the volume and over-doses every treatment thereafter.
- Pump for good filtration: the volume divided by a two-hour turnover, so the example pond wants roughly an 1,800 litre-per-hour pump. Wildlife ponds without fish need no pump at all.
- Liner size needed: length plus twice the depth plus 60cm of overlap, by the same for width, so the example needs a sheet about 4.8 x 3.8m. Deeper is better: 60cm-plus keeps temperatures stable and protects fish from frost, with shelved margins at 20 to 30cm for plants.
- Depth profile (advanced): if you only know the maximum depth, choose a profile and the calculator scales the volume down (x0.85 for steep sides, x0.7 for a shelved pond) while keeping the liner sized to the full depth.
- Pump turnover (advanced): edit the two-hour default: koi ponds want a turnover every hour or two, a lightly stocked goldfish pond can manage every three.
- Pump rating allowing for head (advanced): a pump's rated flow falls the higher it lifts to a filter or waterfall, by roughly 20% per metre for typical pond pumps, so the card shows the rated flow to buy. Check the manufacturer's flow curve for the exact model.
- Stocking guide (advanced): a common UK rule is 50cm of goldfish (total body length, allowing for growth) per 1,000 litres, or about one adult koi per 1,000 litres. The sub-line also gives the number of per-1,000-litre doses for treatments and clarifiers, which is why keepers write the volume on the shed wall.
- Liner and underlay cost (advanced): liner area x your price per m2 with an adjustable overlap. Butyl liners are typically GBP 8 to GBP 15 per m2, EPDM and PVC less, and underlay (needed to protect against stones and roots) adds the same area again.
- Cost to fill (advanced): the volume in cubic metres x your metered water rate (combined water and sewerage is commonly GBP 2 to GBP 4 per m3 in England and Wales). A hose delivers roughly 1,000 litres an hour, and tap water should be left to dechlorinate before fish go in.
Further reading: Royal Horticultural Society.