Pipe Volume Calculator

Treat the pipe as a cylinder. Take the inner radius in feet (half the inner diameter, divided by 12 to convert inches to feet), square it, multiply by pi, then multiply by the length in feet. That gives cubic feet, which you multiply by 7.48052 to get gallons. This calculator does all of that for you the moment you type.

Always use the actual inner diameter for an accurate volume. Nominal (trade) sizes are labels, not true bores — a '1 inch' pipe rarely has a 1 inch inside diameter. Wall thickness from the schedule (Sch 40, Sch 80) and the material change the real opening, so check a dimension chart for your exact pipe and enter that bore. The quick-pick buttons are a convenient starting point, not exact bores.

Nominal pipe size (NPS) is a naming standard that roughly describes the pipe, while the inner diameter is the real measured opening the water flows through. A higher schedule means thicker walls and a smaller inner diameter for the same nominal size, which is why two pipes labeled the same can hold different volumes.

Enter a flow rate in gallons per minute (GPM) and the calculator divides the pipe's total gallons by that rate to estimate fill time in minutes. It assumes a steady flow and an empty pipe to start, so real-world fill time can vary with pressure, fittings, and air in the line.

No. The calculation is for a straight cylindrical run of pipe at the inner diameter you enter. Fittings, valves, and tanks add volume that this tool does not include, so add those separately for a full-system total if precision matters.

The calculator shows all three at once. Internally it computes cubic feet first, converts to gallons by multiplying by 7.48052, then to liters by multiplying gallons by 3.78541. You can copy the full breakdown with the Copy Results button.

This version takes the inner diameter in inches and length in feet, and reports gallons, cubic feet, and liters. If your pipe is sized in millimeters, convert the bore to inches (divide mm by 25.4) and the length to feet before entering them, and read the liters output for a metric result.

Yes, the calculator is completely free with no signup required. Your inputs are saved locally in your browser so they persist between visits — nothing is uploaded to a server. Clearing your browser data will erase your saved values.