How it works
A pipe is a cylinder, so its volume is the area of the bore times the length. The bore area is π ÷ 4 times the inside diameter squared. Convert cubic inches to gallons by dividing by 231, the number of cubic inches in a US gallon.
Use the inside diameter, not the nominal or outside size. Schedule 40 pipe of a given nominal size has a standard inside diameter, which is built in. For copper tube, PEX, or any other pipe, enter the actual inside diameter.
Worked example
100 feet of 1-inch Schedule 40 pipe:
- Inside diameter = 1.049 in
- Volume per foot = π ÷ 4 × 1.049² × 12 in ÷ 231 in³/gal = 0.0449 gal/ft
- Volume = 0.0449 gal/ft × 100 ft = 4.49 gal
- Weight of water = 4.49 gal × 8.34 lb/gal = 37.4 lb
| Input | Value |
|---|---|
| Pipe size | 1" Schedule 40 |
| Inside diameter (own value) | 1.049 in |
| Pipe length | 100 ft |
| Result | Value |
|---|---|
| Volume of the run | 4.49 gal |
| Volume per foot | 0.0449 gal |
| Volume in cubic feet | 0.6 ft³ |
| Weight of water inside | 37.4 lb |
Schedule 40 inside diameter and gallons per foot
| Nominal size | Inside diameter (in) | Gallons per foot |
|---|---|---|
| Own value | - | - |
| 1/2" | 0.622 | 0.0158 |
| 3/4" | 0.824 | 0.0277 |
| 1" | 1.049 | 0.0449 |
| 1-1/4" | 1.380 | 0.0777 |
| 1-1/2" | 1.610 | 0.1058 |
| 2" | 2.067 | 0.1743 |
| 2-1/2" | 2.469 | 0.2487 |
| 3" | 3.068 | 0.3840 |
| 4" | 4.026 | 0.6613 |
| 6" | 6.065 | 1.5008 |
Show the schedule 40 inside diameter and gallons per foot table
| Nominal size | Inside diameter (in) | Gallons per foot |
|---|---|---|
| Own value | - | - |
| 1/2" | 0.622 | 0.0158 |
| 3/4" | 0.824 | 0.0277 |
| 1" | 1.049 | 0.0449 |
| 1-1/4" | 1.380 | 0.0777 |
| 1-1/2" | 1.610 | 0.1058 |
| 2" | 2.067 | 0.1743 |
| 2-1/2" | 2.469 | 0.2487 |
| 3" | 3.068 | 0.3840 |
| 4" | 4.026 | 0.6613 |
| 6" | 6.065 | 1.5008 |
Assumptions and limits
- Uses the nominal inside diameter. Wall thickness varies within tolerance, and plastic pipe made to Schedule 40 may differ slightly, so measure or check the marking for critical work.
- Water weight is 8.34 lb per gallon near room temperature; it varies slightly with temperature.
- Straight pipe only. Fittings, valves, and tanks add volume that is not included.
Common questions
How many gallons are in 100 feet of 1-inch pipe?
About 4.5 gallons for 1-inch Schedule 40, whose inside diameter is 1.049 in.
Why does nominal size not match the real diameter?
Nominal pipe size is a name. The bore depends on wall thickness, which is set by the schedule, so use the inside diameter.
How do I convert to liters?
Switch the unit toggle to Metric; the result then shows liters and cubic meters.
Does it include fittings?
No. Add the volume of tanks, heat exchangers, and large fittings separately.
Sources
- ASME B36.10M nominal Schedule 40 inside diameters; volume of a cylinder.
- 1 US gallon = 231 cubic inches; water at about 8.34 lb per gallon.
Updated 2026-09-30