By Zencalcy Editorial TeamLast reviewed About us
A pipe holds less than it looks: a 1-inch line holds about 0.041 gallons per foot, so 100 feet holds just over 4 gallons. That matters for flushing, winterising, dosing and pump priming — and for knowing how long a line takes to deliver hot water.
Water held in a pipe, and what it weighs.
V = π × (d ÷ 2)² × L
Use the inside diameter. Nominal pipe sizes are not diameters: 1-inch schedule 40 PVC has an inside diameter of about 1.05 inches, while 1-inch copper is 1.025. One cubic foot of water weighs 62.4 lb.
| Symbol | Meaning |
|---|---|
| d | Inside diameter. |
| L | Pipe length. |
| V | Internal volume. |
With a 1.05 inch ID, 100 ft holds about 4.5 gallons — roughly 37 lb of water.
Continue with the Pool Calculator, Round Pool Volume Calculator, Pond Calculator, or the Tank Volume Calculator — or browse more tanks, pools & flow and all construction calculators.
About 0.045 gallons for a 1.05 inch ID. A 2-inch line holds roughly 0.17 gallons per foot.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026