not enough information. size and shape of pipe needed.
A two inch pipe can hold 0.1632 gallons per foot. It takes slightly over 6 feet of two inch pipe to hold one gallon of water.
20
1/8" per foot.
About 1.25 gallons per minute.
The pipe diameter doesn't matter. If the pipe is discharging a cubic foot per second then it will discharge 86400 cubic feet in a day, because that is the number of seconds in one day. One acre foot is 43560 cubic feet, so the pipe discharges 86400/43560 ~= 1.98 acre feet. On the other hand, if you meant to say the water velocity exiting the pipe is 1 foot per second (not one cubic foot per second), then, assuming you have the average water velocity, you need to figure the flow rate first. The pipe has a radius of 2 in. so its cross sectional area is pi*r^2 = pi*4 ~= 12.57. So a volume of 12.57 in.^2 * 12 in. is discharged per second, which is ~ 150.80 in.^3 or about 0.09 cubic feet. From there it's the same as above. On the other other hand, if your water velocity is not the average over the cross sectional area but instead a point velocity, say at the middle of the stream of water, then you need to figure the average velocity. You'll need a hydraulics book with pipe roughness coefficients for that.
For a 3 foot diameter pipe, 52.9 US gallons per foot of length.
2.61153 gallons.
In a pipe with diameter 8 ft, there will be just over 376 US gallons per foot.
0.6528 gallon per foot (rounded)
0.3672 gallon per foot of pipe.
0.212 331 gallons per foot.
A 12 inch diameter round pipe will hold 4.89 UK gallons or 5.88 US gallons per foot.
36.83 u.s. gallons of water in 1 ft. of 30" pipe
0.255 gallons per foot of pipe. A 10 ft long pipe that size holds 2.55 gallons.
231 cubic inches. So 0.832674 Gallons.
Pipe is generally cylindrical and the dimension refers to the inside diameter. One cubic foot contains 7.48 gallons. The volume of a one foot long 20" diameter pipe is: pi(1.667/2)^2 = 2.18 cubic feet. At 7.48 gallons per cubic foot the total volume is 16.3 gallons.
16" pipe per foot = 9.17 Gallons for 16" SCH 40 pipe we just had to figure it out in our engineering department was looking for a short cut and ran across your post.