Per run: — gal | Runs: — | Cubic inches: — | Weight: — kg
Result Summary
| Pipe | — |
| Inside diameter | — |
| Total length | — |
| Total volume | — |
| Liquid weight | — |
Pipe Volume and Inside Diameter by Size (per 100 ft, water)
| Nominal | Sch 40 ID | Sch 40 gal | Sch 80 ID | Sch 80 gal |
|---|---|---|---|---|
| 1/2 in. | 0.622 | 1.58 | 0.546 | 1.22 |
| 3/4 in. | 0.824 | 2.77 | 0.742 | 2.25 |
| 1 in. | 1.049 | 4.49 | 0.957 | 3.74 |
| 1-1/4 in. | 1.380 | 7.77 | 1.278 | 6.66 |
| 1-1/2 in. | 1.610 | 10.58 | 1.500 | 9.18 |
| 2 in. | 2.067 | 17.43 | 1.939 | 15.34 |
| 3 in. | 3.068 | 38.4 | 2.900 | 34.3 |
| 4 in. | 4.026 | 66.1 | 3.826 | 59.7 |
Schedule 80 has thicker walls, so a smaller inside diameter and less volume than Schedule 40 at the same nominal size.
How Much Water Is in a Pipe?
The water in a pipe is simply the inside cross-section area multiplied by the length. Because the area depends on the square of the inside diameter, a small jump in pipe size makes a big difference in volume: a 1 in. line holds nearly three times the water of a 1/2 in. line over the same distance. The calculator above uses the true inside diameter for your material and schedule, multiplies by length and the number of runs, and reports the result in gallons, liters, cubic feet, and weight. This is useful for filling and flushing systems, dosing antifreeze, sizing an expansion tank, or estimating how long a recirculation loop takes to turn over.
Pipe Volume by Size
The reference table above lists gallons per 100 feet for common sizes in both Schedule 40 and Schedule 80. As a quick mental model: 1/2 in. holds roughly 1.5 gallons per 100 ft, 3/4 in. about 2.8, and 1 in. about 4.5. For a whole house with several long runs, multiply by your run count using the number-of-runs field. For partially filled drain lines, switch to partial fill and set the depth so the tool uses the correct circular-segment area instead of a full circle.
Pipe Schedule and Inside Diameter
Nominal pipe size is a label, not the real bore. Schedule sets the wall thickness: a higher schedule means thicker walls and a smaller inside diameter for the same nominal size, so Schedule 80 holds less than Schedule 40. Copper is sized by type (K, L, M) rather than schedule, and PEX has a noticeably smaller inside diameter than rigid pipe at the same nominal size. Selecting a material and schedule fills in the correct inside diameter automatically, and you can override it with a measured value if you know the exact bore.
Frequently Asked Questions
How many gallons in 100 ft of 3/4 in. pipe? About 2.8 gallons for Schedule 40, a bit less for Schedule 80 or PEX.
Does antifreeze change the volume? No, but it changes the weight. Glycol mixtures are slightly denser than water, which the liquid-type setting accounts for.
Why is PEX volume lower? PEX has thicker walls relative to its nominal size, giving a smaller bore and less internal volume than copper or PVC.
How do I handle multiple sizes? Calculate each size separately and add the totals, or use runs for identical lengths of the same pipe.