Free pond calculator
To calculate pond volume, multiply length x width x average depth in feet, then multiply by 7.48 to get US gallons (for a round pond use 3.14 x radius² x depth; for an oval, 3.14 x half the length x half the width x depth). This free calculator does that for rectangle, circle, oval and kidney-shaped ponds with shelves, then sizes your pond liner, pump and waterfall flow, and pond salt dose.
Pond volume calculator
Measure your pond and fill in the shape. Everything runs in your browser and is saved on this device only.
Try an illustrative example
Volume (US gallons)
995 US gal
Liters
3,766 L
Cubic feet
133 cu ft
Surface area
66.5 sq ft
Water weight
8,298 lb
Kidney / irregular: surface area 66.5 sq ft x average depth 2 ft x 7.48 = US gallons. Water weight uses about 8.34 lb per US gallon (1 kg per liter). Irregular ponds are an estimate; more readings give a better average.
Pond liner calculator
Typical 1-2 ft per side.
Liner size
17 x 15 ft
Liner area
255 sq ft
Liner length = max length 10 ft + 2 x max depth 2.5 ft + 2 x overlap 1 ft = 17 ft. Width = 8 ft + 2 x 2.5 ft + 2 x 1 ft = 15 ft. Buy underlayment the same size, and round up to the next stock liner size.
The liner uses the longest length, widest width and deepest point, not the averages. Some suppliers write the formula as 2 x depth + 2 ft, which is the same as the default 1 ft overlap per side; use more overlap if your edge needs it.
Pond pump size calculator
Leave blank or 0 for none. Measure the spillway lip, not the frame rocks.
Height from the pond surface to the top of the waterfall or filter.
Circulation (1-1.5x per hour)
990 GPH - 1,490 GPH
3,770 LPH - 5,650 LPH
Waterfall / stream add-on
None
Total target flow
990 GPH - 1,490 GPH
3,770 LPH - 5,650 LPH
Pump ratings drop with head height. Enter your vertical lift, then pick a pump whose flow curve delivers the target at that height, not just at 0 ft.
Rules of thumb: pumps are commonly sized to turn the whole pond over about once an hour (Aquascape), every 1-2 hours where light stocking and filtration allow, and 1-2 times an hour for koi. Waterfalls are sized by spillway width: about 100 GPH per inch for a light sheet, 1,500 GPH per foot (125 per inch) for an average residential fall, 3,000 GPH per foot for a heavy commercial look. The total adds the waterfall flow on top of circulation, which is the conservative case. Check your filter's maximum flow too.
Pond salt & treatment dosing
| Level | Pounds | Kilograms |
|---|---|---|
| 0.1%General tonic | 8.3 lb | 3.77 kg |
| 0.3%Upper limit for routine use | 24.9 lb | 11.3 kg |
| 0.2%Custom | 16.6 lb | 7.53 kg |
Salt by weight: 0.1% is about 0.83 lb per 100 US gallons (1 kg per 1,000 L); 0.3% is about 2.5 lb per 100 gallons.
Enter the dose printed on any pond treatment or bacteria product to scale it to your pond.
Example: a label that says 5 ml per 100 gallons. Enter 5, ml, 100, US gal.
Liner length = max length + 2 x max depth + 2 x overlap. Liner width = max width + 2 x max depth + 2 x overlap. Use the deepest point, not the average, and allow 1-2 ft (0.3-0.6 m) of overlap per side to anchor under edging stones.
Turn the whole pond over about once an hour (every 1-2 hours for lightly stocked plant ponds, 1-2 times an hour for koi). Add waterfall flow by spillway width, then check the pump's flow curve at your head height.
Step 1
Choose rectangle or square, circle, oval, or kidney / irregular. Each shape has its own surface area formula.
Step 2
Measure the length and width of the water surface in feet or meters. For an irregular pond, take several readings of each.
Step 3
Measure the depth at several spots, including shelves and the deepest point, and average them. For shelves, note the share of the area at each depth.
Step 4
Surface area x average depth gives the volume in cubic feet or cubic meters.
Step 5
Multiply cubic feet by 7.48 for US gallons, or cubic meters by 1,000 for liters. Divide liters by 4.546 for UK gallons.
Multiply length x width x average depth in feet to get cubic feet, then multiply by 7.48 for US gallons. For a round pond use 3.14 x radius x radius x depth; for an oval use 3.14 x half the length x half the width x depth. A 10 x 8 ft pond that averages 2 ft deep holds about 160 cu ft, or roughly 1,197 US gallons (4,531 liters).
Liner length = the pond's longest length + 2 x its deepest depth + 2 x the overlap at the edge; liner width = widest width + 2 x deepest depth + 2 x overlap. Allow about 1-2 ft (0.3-0.6 m) of overlap per side. A 10 x 8 ft pond, 2 ft deep with 1 ft overlap, needs a 16 x 14 ft liner and the same size underlayment.
A common rule is a pump that moves the whole pond volume about once an hour: a 1,000-gallon pond needs roughly 1,000 GPH. Lightly stocked plant ponds can run once every two hours; koi ponds often run 1-2 turnovers an hour. Add waterfall flow by spillway width (about 1,500 GPH per foot for an average residential fall) and choose a pump that delivers the total at your head height, not at 0 ft.
Measure the length at several points along the pond, the width at several points across it, and the depth at several spots, then average each set and multiply them. More readings give a better estimate. For ponds with plant shelves, split the pond into depth zones and add them up, which this calculator does for you.
Salt is measured by weight: 0.1% is about 0.83 lb per 100 US gallons (1 kg per 1,000 liters) and 0.3% is about 2.5 lb per 100 gallons. Use pond salt, add it gradually, and do not exceed 0.3% for routine use. Salt does not evaporate, so top-offs need none, and many pond plants are damaged above about 0.1%. Always follow the product label.
Ponds are measured in feet with uneven depths and sloped sides, so you average several depth readings, while aquariums are glass boxes measured in inches. Ponds also need liners, outdoor pumps sized for head height and waterfalls. For a glass tank, use the Aquarium Volume Calculator instead. Open the Aquarium Volume Calculator.
Volume for glass tanks: rectangle, bow front, cylinder, hexagon and more.
Freshwater aquarium salt doses by tank volume and purpose.
Dilute a stock treatment to the strength you need.
Convert between ppm, mg/L and doses for a given water volume.
Size a heater for an indoor tank or overwintering tub.
Work out how much gravel or sand to buy.
Keep a reef tank or pond aquarium indoors? Track water tests and maintenance with My Reef Log.