Find how much water a pipe holds. Pick a nominal size from 1/2 to 12 inches in Schedule 40 or 80 — the inside diameters come from the ASME B36.10M table — or type any inside diameter in inches or millimeters, then enter the length. Add as many segments as your run has, and the calculator totals the volume in US gallons, liters, and cubic feet along with the weight of the water.
Filling something bigger than a pipe? The pool volume calculator and aquarium volume calculator use the same gallon math, and the French drain calculator sizes the gravel and perforated pipe for a drainage trench.
Frequently asked questions
How do you calculate the volume of a pipe?
A pipe's bore is a cylinder, so volume = π × (inside diameter ÷ 2)² × length. Keep the units consistent: with the diameter and length both in feet you get cubic feet, and multiplying by 7.4805 converts that to US gallons (or by 28.317 to liters). For example, a 1-inch inside diameter holds 0.0408 gallons per foot, so 100 feet holds about 4.1 gallons. This calculator does the conversion for every segment you add and totals them, so you can model a main line plus its branches in one go.
Why does nominal pipe size not match the actual diameter?
Nominal pipe size (NPS) is a label, not a measurement. For NPS 1/8 through 12 the outside diameter is fixed by ASME B36.10M — a 1-inch pipe is actually 1.315 inches outside — and the schedule sets the wall thickness. Because the outside stays constant, a thicker schedule shrinks the inside: 1-inch Schedule 40 has a 1.049-inch bore, while Schedule 80 has 0.957. That is why the calculator asks for the schedule, and why you should measure the bore, not the outside, if you enter a diameter by hand.
Does this work for PVC, copper, or PEX pipe?
Schedule 40 and 80 PVC (ASTM D1785) use the same outside diameters and minimum wall thicknesses as the steel pipe table, so the nominal sizes here are a close match for PVC. Copper tube (Types K, L, and M) and PEX use completely different sizing systems — for example, 3/4-inch Type L copper has a bore of about 0.785 inches and 3/4-inch PEX is closer to 0.68 inches. For those, switch the segment to Inside diameter and enter the bore from the manufacturer's spec sheet.
How much does the water in a pipe weigh?
Water weighs about 8.345 pounds per US gallon (roughly 1 kilogram per liter). Multiply the gallons by 8.345 to get pounds — 100 feet of 4-inch Schedule 40 pipe holds about 66 gallons, which is roughly 550 pounds of water. That matters when you size pipe hangers and supports, calculate the load on a roof or a deck from a filled line, or work out how much water you will drain when you open a system for repair. Hot water is a little lighter — about 3% at 180 °F — so the figure errs slightly high for hot lines.
What is this useful for?
Knowing the volume of a pipe run helps you dose chemicals for disinfecting a well or a potable water line, figure how much antifreeze a hydronic loop or an RV winterizing job needs, estimate how long it takes hot water to reach a faucet, plan the fill volume of a sprinkler main, or calculate the water weight a support has to carry. Add a segment for each diameter in the run and the calculator totals gallons, liters, cubic feet, and weight.