Contractor Calculator · Plumbing
Pipe Volume Calculator: Gallons, Cubic Feet, and Water Weight
Nominal size is a label, not a measurement. Pick the material and schedule and the gallons, water weight and fill time update as you type.
Pricing the repipe? Estimate it from a photo in six seconds.
Inside diameters from published maker and association dimension tables, read September 11, 2026. Water at 8.34 lb per gallon.
How the pipe volume calculator works
A pipe is a cylinder, so volume is pi times the inside radius squared times the length. One part is hard: the inside radius is the number nobody has on hand, because pipe is sold by nominal size and nominal size is a label.
Half inch Schedule 40 PVC measures 0.622 in inside. Half inch Type L copper measures 0.545 in. Feed 0.5 into Schedule 40 and the answer is low by a third.
Worked example: 100 feet of 1 inch Schedule 40
The published bore is 1.049 in, so the radius is 0.5245 in and the bore area 0.864 square inches. Times 1,200 inches of run: 1,037 cubic inches.
Divide by 231 and that is 4.49 gallons, or 0.6 cubic feet. At 8.34 lb a gallon the water weighs 37.4 lb, and at 5 gpm the run fills in 54 seconds.
SimplyWise Cost Estimator turns the same run into a priced estimate from one photo.
Inside diameter by size and schedule
Published dimensions, in inches, off maker and association tables.
| Nominal | PVC Sch 40 | PVC Sch 80 | Copper K | Copper L | Copper M |
|---|---|---|---|---|---|
| 1/2 in | 0.622 | 0.546 | 0.527 | 0.545 | 0.569 |
| 3/4 in | 0.824 | 0.742 | 0.745 | 0.785 | 0.811 |
| 1 in | 1.049 | 0.957 | 0.995 | 1.025 | 1.055 |
| 1-1/4 in | 1.380 | 1.278 | 1.245 | 1.265 | 1.291 |
| 1-1/2 in | 1.610 | 1.500 | 1.481 | 1.505 | 1.527 |
| 2 in | 2.067 | 1.939 | 1.959 | 1.985 | 2.009 |
Read one row across. At 2 in nominal the bore swings from 1.939 in to 2.067 in, and volume moves with its square.
Why Schedule 80 holds less
Schedule is wall thickness, not size. Both share an outside diameter, so the same fittings fit either. The thicker wall comes out of the bore.
Two inch Schedule 40 runs a 0.154 in wall and a 2.067 in bore. Schedule 80 runs 0.218 in and 1.939 in. Six percent off the diameter is twelve percent off the volume.
Turn the takeoff into a signed quote
Sizing the pipe is the easy half. SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds, with material and labor line items. Pricing is $29.99/mo or $239.99/yr, about $20/mo on annual, with a 7-day free trial.
Copper Type K, Type L and Type M
Copper water tube holds one outside diameter per size, always an eighth of an inch over nominal, with three wall thicknesses inside it. Type K is heaviest, Type L is the common service wall, Type M is thinnest.
Three quarter inch copper runs a 0.875 in outside diameter in all three. Inside: Type K 0.745 in, Type L 0.785 in, Type M 0.811 in. That is 2.26 gallons per 100 ft against 2.51 against 2.68, and on a recirculating loop the wall sets what you pay to keep it hot.
Water weight is the number that moves a job
Water weighs 8.34 lb a gallon, off a published density near 62.4 lb per cubic foot. Nobody thinks about it on a half inch branch. It matters once the run is big.
A hundred feet of 4 in Schedule 40 holds 66.13 gallons, so the pipe gains 551 lb the second it fills. Hangers and a wood joist both care.
Run the pipe volume calculator in this order
-
Read the size and the schedule off the pipe
The print carries both. Nominal size alone does not give you the bore.
-
Look up the published inside diameter
Use the maker or association dimension table. Never a rounded nominal number.
-
Multiply the bore area by the run length
Pi times radius squared times length in inches. Keep every unit in inches.
-
Convert, then weigh it
Divide by 231 for gallons or 1,728 for cubic feet, then gallons by 8.34 for pounds.
Keep reading
Sources
PVC inside diameters
- Charlotte Pipe and Foundry, Dimensional Catalog, Plastics Pressure Systems (Pipe Data pages for PVC Schedule 40 Plain End and PVC Schedule 80 Plain End, both marked ASTM D 1785; average OD and minimum wall per row; read 2026-09-11).
Copper tube inside diameters
- Copper Development Association, Copper Tube Handbook, CDA Publication A4015-26/24 (Tables 14.2a, 14.2b and 14.2c, dimensions and physical characteristics of copper tube Type K, Type L and Type M; read 2026-09-11).
Units and water density
- NIST Handbook 44, 2026, Appendix C, General Tables of Units of Measurement (1 gallon = 231 cubic inches exactly; read 2026-09-11).
- USGS Water Science School, Water Density (62.424 lb per cubic foot at 39.2 F, which works out to 8.34 lb per gallon; read 2026-09-11).
Product
- SimplyWise Cost Estimator, App Store (4.8 rating; verified 2026-09-09).
Common questions on the pipe volume calculator
Volume and gallons
How do I calculate the volume of water in a pipe?
Multiply pi by the inside radius squared by the length, all in inches. Divide by 231 for gallons or 1,728 for cubic feet.
How many gallons are in 100 feet of 1 inch pipe?
4.49 gallons in Schedule 40 PVC, on a 1.049 in bore. Schedule 80 holds 3.74 and Type L copper 4.29.
Is nominal pipe size the same as inside diameter?
No. Half inch Schedule 40 PVC measures 0.622 in inside, half inch Type L copper 0.545 in. Use the published dimension.
Schedule, material and weight
Does Schedule 80 hold less water than Schedule 40?
Yes. Both share an outside diameter, so the thicker wall comes out of the bore. Two inch drops from 17.43 gallons per 100 ft to 15.34.
How much does the water in a pipe weigh?
8.34 lb a gallon. A hundred feet of 4 in Schedule 40 holds 66.13 gallons, so the run gains 551 lb.
Can SimplyWise price a repipe from a photo?
Yes. SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds, with material and labor line items. Free to try, $29.99/mo.
Turn the pipe takeoff into a signed quote.
Snap a photo and get an itemized estimate in about 6 seconds. Free to try.