How many gallons of water will a 20 foot pipe hold if it is 3 inches in diameter?

Question

How many gallons of water will a 20 foot pipe hold if it is 3 inches in diameter?

2 Answers

Answer Question

Answer 1

Volume of a cylinder = circular area x length. Circular area = Pi x r^2 (pie are square) Pi = 3.14 r = radius or 1/2 diameter. Divide diameter (3) by 2 and square that number. Multiply that by Pi (3.14) to find circular area in square inches. Convert 20 feet to inches by multiplying by 12 (1 foot = 12 inches) Now multiply that by circular area and answer will be in cubic inches. 1 gallon = 231 cubic inches. Divide 231 into last answer for gallons of water.

Answer 2

For this, we need to look at the volume contained in the pipe. We'll assume for now that the 3 inch diameter is the internal diameter, to make this simpler. Thus, we have a 1.5 inch radius, so the cross-sectional area of the pipe would be pi*(1.5in)^2 = 2.25pi in^2. To obtain the volume of a cylinder, we then take the height of the cylinder multiplied by the base area (as with all regular prisms). Thus the 20 foot (20feet*12in/ft = 240in) height multiplied by the base area is 540pi in^3. This turns out to be near 1696.46in^3. We then apply the unit conversion of ~0.554 fluid ounces/in^3 to 1696.46in^3 and we have 939.84 fluid ounces. This finally is applied to the conversion 1 gallon/128fluid ounces to achieve 7.3429 gallons.Alternatively, you can type this into google to get: 540 * pi (in^3) = 7.34398283 US gallons.Hope this helps.