A pipe is sold by its nominal size, which is not its inside diameter. For PVC the outside diameter is fixed by size and the wall gets thicker from PVC Schedule 40 to PVC Schedule 80, so the same nominal pipe holds less water in PVC Schedule 80. The calculator takes the maker's outside diameter and wall thickness to find the bore.
How to use this calculator
- Choose PVC Schedule 40 or PVC Schedule 80, or Other to type the inside diameter of copper, PEX, steel or any other pipe.
- Pick the nominal size printed on the pipe.
- Enter the length of the run. Add the lengths of every section if the pipe turns corners.
Worked examples
A two-inch PVC run
Pipe: PVC Schedule 40 · Nominal size: 2 in · Pipe length: 100 ft
- Water in the pipe
- 17.43 US gallons
- Volume
- 2.33 cubic feet
- Per foot of pipe
- 0.174 US gallons
- Weight of the water
- 145 lb
- Inside diameter used
- 2.07 in
A four-inch drain line
Pipe: PVC Schedule 40 · Nominal size: 4 in · Pipe length: 60 ft
- Water in the pipe
- 39.68 US gallons
- Volume
- 5.3 cubic feet
- Per foot of pipe
- 0.661 US gallons
- Weight of the water
- 331 lb
- Inside diameter used
- 4.03 in
PVC Schedule 80 pipe
Pipe: PVC Schedule 80 · Nominal size: 1 in · Pipe length: 200 ft
- Water in the pipe
- 7.47 US gallons
- Volume
- 0.999 cubic feet
- Per foot of pipe
- 0.037 US gallons
- Weight of the water
- 62.33 lb
- Inside diameter used
- 0.96 in
Any pipe by its inside diameter
Pipe: Other: enter the inside diameter · Inside diameter: 0.75 in · Pipe length: 150 ft
- Water in the pipe
- 3.44 US gallons
- Volume
- 0.46 cubic feet
- Per foot of pipe
- 0.023 US gallons
- Weight of the water
- 28.71 lb
- Inside diameter used
- 0.75 in
How the volume is worked out
The water in a pipe is a long cylinder: the area of the bore times the length. The bore is the outside diameter less twice the wall, so the calculator subtracts the maker's minimum wall from its average outside diameter. Real walls run a little thicker than the minimum, so the answer can read slightly high.
A gallon of water weighs 8.34 lb per US gallon, so the weight follows from the gallons. That matters when a long pipe full of water hangs from hangers or sits on a deck.
Why it is useful
- Dosing a treatment or antifreeze for a whole loop.
- Knowing how long it takes hot water to reach a tap: the water already in the pipe has to run out first.
- Filling an irrigation main, a pond line or a heating loop.
- Checking that supports can carry a full pipe.
Common questions
How do I calculate the volume of a pipe?
Multiply the area of the inside circle by the length. Halve the inside diameter, square it, multiply by pi, and multiply by the length in the same units. Then convert cubic feet or cubic inches to gallons, or let the calculator do it.
Why does PVC Schedule 80 hold less water than PVC Schedule 40?
Both have the same outside diameter for a nominal size, but PVC Schedule 80 has a thicker wall, so the inside is smaller and holds less.
Is the nominal size the inside diameter?
No. For PVC and steel the nominal size is a trade name, and the inside diameter is somewhat larger or smaller depending on the schedule. Use the size list above, or measure the inside of a cut end.
How much does the water in a pipe weigh?
A gallon of water weighs 8.34 lb per US gallon. The calculator multiplies that by the gallons in the pipe, so add the weight of the empty pipe for the total load.