# Pipe Volume Calculator

Calculate the water volume inside any pipe from its diameter and length. Get results in gallons, liters, and cubic feet plus water weight for plumbing.

## What this calculates

Whether you are draining a plumbing system, sizing a water supply, or estimating irrigation capacity, knowing the volume of water inside a pipe is essential. Enter the pipe's inner diameter and length to calculate the total volume in gallons, liters, and cubic feet, plus the weight of the water.

## Inputs

- **Pipe Inner Diameter** (in) — min 0 — Inside diameter of the pipe
- **Pipe Length** (ft) — min 0 — Total length of the pipe run

## Outputs

- **Volume** (gallons) — Water volume in US gallons
- **Volume** (liters) — Water volume in liters
- **Volume** (ft³) — Internal pipe volume
- **Water Weight** (lbs) — Weight of water filling the pipe

## Details

The volume of a pipe is calculated using the cylinder formula: V = π x (diameter/2)² x length. The result in cubic inches is then converted to gallons by dividing by 231 (the number of cubic inches in a US gallon).

Use the inner diameter (ID) of the pipe, not the outer diameter (OD). The nominal pipe size (e.g., "1-inch pipe") doesn't match the actual inner diameter. For example, a 1-inch Schedule 40 PVC pipe has an actual ID of 1.029 inches. Check the manufacturer's specifications for exact ID values.

Water weighs 8.34 pounds per gallon at room temperature. This weight is important for structural support calculations. A 100-foot run of 4-inch pipe holds over 40 gallons, weighing more than 340 pounds. Always account for water weight when routing pipes through ceilings or along walls.

## Frequently Asked Questions

**Q: Should I use the inner or outer diameter?**

A: Always use the inner diameter (ID) for volume calculations. The ID is the open space where water actually flows. The nominal pipe size (like '1-inch pipe') is just a trade designation and doesn't reflect the actual inner diameter.

**Q: What is the inner diameter of common residential pipe sizes?**

A: Common Schedule 40 PVC inner diameters: 1/2" pipe = 0.622" ID, 3/4" pipe = 0.824" ID, 1" pipe = 1.029" ID, 1-1/2" pipe = 1.590" ID, 2" pipe = 2.047" ID, 3" pipe = 3.042" ID, 4" pipe = 4.026" ID.

**Q: How much does the water in a pipe weigh?**

A: Water weighs 8.34 pounds per US gallon (1 kg per liter). A 100-foot run of 2-inch pipe holds about 16.3 gallons, weighing approximately 136 pounds. This weight must be considered for pipe support spacing and structural calculations.

**Q: Does this calculator work for gas pipes?**

A: Yes, the volume calculation works for any fluid. However, gas volume depends heavily on pressure and temperature (use the Ideal Gas Law). This calculator gives the physical volume of the pipe interior, which is the starting point for gas capacity calculations.

**Q: How do I calculate flow rate through a pipe?**

A: Flow rate (GPM) depends on velocity and pipe area: GPM = Area (sq in) x Velocity (ft/sec) x 0.3208. Typical residential water velocity is 5-8 ft/sec. A 3/4-inch pipe at 6 ft/sec flows about 6 GPM.

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Source: https://vastcalc.com/calculators/construction/pipe-volume
Category: Construction
Last updated: 2026-04-21