How does the calculation work?
Volume = surface area × average depth
A rectangular pond 10 ft by 6 ft and 2 ft deep holds 120 ft³. With 7.48 gallons in every cubic foot, that is about 898 gallons.
Ponds are rarely the same depth all over. Measure the depth in several places and use the average for the most accurate result.
Planning the rest of the job? Use the Landscape fabric calculator and the Irrigation water calculator too.
Liner size
A liner needs to cover the length and width, go down both sides and leave an edge to tuck under stones.
Liner length
Pond length + 2 × depth + 2 ft (60 cm)
Liner width
Pond width + 2 × depth + 2 ft (60 cm)
Underlay
Same size as the liner
How do I choose a pump?
A good rule is a pump that moves the whole pond volume once an hour. With fish, aim for at least once every one to two hours. If the pump also feeds a waterfall or filter some height above the pond, choose one rated for that extra lift.