Pipe Volume Calculator

A pipe volume calculator returns how much liquid a length of pipe holds, in gallons and cubic feet. It uses the inner diameter to find the cross-sectional area, multiplies by the length, and converts to gallons with the exact 7.48052 gallons per cubic foot. A 4 in. inner diameter pipe, 100 ft long, holds about 65.28 gallons.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Volume

65.28 gal

Breakdown
Volume	65.28 gal
Volume	8.727 cu ft

How to Calculate Pipe Volume

A pipe's interior is a cylinder, so its volume is `π × radius² × length`. Converting the diameter from inches to feet first keeps the units consistent with length, which is already in feet. Multiplying the resulting volume in cubic feet by 7.48052 gives the volume in gallons.

Example: 4 in. inner diameter pipe, 100 ft long

A 4 in. inner diameter pipe, 100 ft long: 1. Diameter in feet: 4 ÷ 12 = 0.333 ft 2. Cross-sectional area: π × (0.333 ÷ 2)² = π × 0.02778 = 0.08727 sq ft 3. Volume: 0.08727 × 100 = 8.727 cu ft 4. Gallons: 8.727 × 7.48052 = 65.28 gal

Pipe Volume: Compare Scenarios

Scenario	Volume	Volume
Small (1 in. line, 50 ft)	2.04 gal	0.273 cu ft
Medium (4 in. line, 100 ft)	65.28 gal	8.727 cu ft
Large (8 in. main, 500 ft)	1,305.60 gal	174.533 cu ft

What Is Pipe Volume?

A pipe volume calculator converts a pipe run's inner diameter and length into the volume of liquid it holds. That's useful for winterizing a system, since you need to know how much water to drain or how much antifreeze to add. It also helps when dosing a chemical treatment into an irrigation line or estimating how much water is in a plumbing run. Use the pipe's actual inner diameter, not its nominal size. Nominal pipe sizes, like "2 inch PVC," often don't exactly match the pipe's true inside diameter. The true inside diameter varies by material and wall thickness, which is the schedule.

Pipe Volume: Pros and Cons

Pros

Uses the exact 7.48052 gallons-per-cubic-foot conversion factor rather than a rounded approximation
Works for any diameter and length, from a small supply line to a large main run
Gives both gallons and cubic feet, useful depending on which unit your specific task (dosing, drainage, capacity) calls for

Cons

Doesn't look up nominal pipe sizes to their actual inner diameter for you. Check your specific pipe's schedule or wall thickness spec sheet for its true inside diameter
Assumes a simple straight, constant-diameter run. A pipe system with multiple diameters or significant fittings needs each section calculated separately, then added together
Doesn't account for a partially full pipe. This calculates volume for a pipe completely full of liquid

Pipe Volume: What a Pro Checks

Use the actual inner diameter for an accurate volume. Nominal sizes like "2 inch PVC" often don't match the true inside diameter, which varies by material and wall thickness (schedule).
If your system mixes diameters, such as a run of larger supply feeding into smaller branch lines, calculate each section separately. Then add the volumes together rather than using one diameter for the whole run.

Frequently Asked Questions

How much water is in a 100 foot length of 4 inch pipe?

About 65.3 gallons, based on the pipe's inner diameter, not its nominal size. A 4 in. inner diameter, 100 ft long pipe holds roughly 8.73 cubic feet. That converts to 65.28 gallons using the exact 7.48052 gallons-per-cubic-foot conversion.

Should I use nominal or actual pipe diameter?

Actual (inner) diameter, for an accurate volume. Nominal pipe sizes are a naming convention, and they often don't exactly match a pipe's true inside diameter. That varies by material, like PVC, copper, or PEX, and by wall thickness or schedule. Check the spec sheet for the actual inside diameter.

How do you convert cubic feet to gallons?

Multiply by 7.48052 US gallons per cubic foot. This calculator applies that conversion automatically after computing the pipe's volume in cubic feet from its diameter and length.

Why would I need to know how much water is in a pipe?

Common reasons include winterizing a plumbing or irrigation system. You need to know how much water to drain, or how much antifreeze to add to protect the line. Other reasons are dosing a water treatment chemical at the correct concentration, or estimating total system capacity.

Does pipe material affect the volume calculation?

Not directly. Volume depends only on inner diameter and length, regardless of whether the pipe is PVC, copper, PEX, or another material. Material matters indirectly, though. Different materials and pressure ratings (schedules) have different wall thicknesses, which changes the actual inner diameter for a given nominal size.

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