GPM to Pipe Size Calculator

Last updated: 19 Apr 2025 | Author: Brij | Review By: Irshad

Share on :

Enter flow rate and flow velocity to convert GPM to pipe diameter in seconds, check flow velocity limits, and get material-specific recommendations.

Flow Rate:

GPM

Flow Velocity:

Pipe Material:

Pipe Size Calculation Results

Minimum Pipe Diameter:

inches

Cross-Sectional Area:

in²

Recommended Nominal Size:

This calculator helps engineers, plumbers, and designers select the correct pipe size based on flow rate (GPM) and flow velocity (FPS/FPM). It ensures efficient fluid transport while avoiding excessive pressure drops or erosion due to high velocity.

How It Works

The calculator uses fluid dynamics principles to determine the minimum pipe diameter required to handle a given flow rate at a specified velocity.

Key Formulas

1. Flow Rate Conversion (GPM to ft³/sec)

To convert Gallons Per Minute (GPM) to Cubic Feet per Second (ft³/sec):

$Q_{cfs} = Q_{gpm} \times 0.002228$

2. Pipe Cross-Sectional Area

Using the continuity equation ( $Q=A×V$ ), solve for area ( $A$ )

$A = \frac{Q_{cfs}}{V_{fps}}$

3. Pipe Diameter Calculation

Convert area to diameter:

$D = 2 \times \sqrt{\frac{A \times 144}{\pi}}$

(where 144 converts ft² to in²)

4. Velocity Check

Ensure velocity stays within material limits:

PVC: ≤ 5 FPS
Copper: ≤ 8 FPS
Steel/HDPE: ≤ 10 FPS

Example Calculation

Problem:

Flow Rate (Q): 120 GPM
Velocity (V): 6 FPS
Material: PVC

Solution Step by Step:

Convert GPM to ft³/sec:

$Q_{cfs} = 120 \times 0.002228 = 0.2674 \text{ ft³/sec}$

Calculate required area:

$A = \frac{0.2674}{6} = 0.0446 \text{ ft²}$

Find diameter (inches):

$D = 2 \times \sqrt{\frac{0.0446 \times 144}{\pi}} = 3.26 \text{ inches}$

Recommended Size: 4" PVC (next standard size).

Why This Matters

Prevents erosion from high-velocity flow.
Optimizes cost by avoiding oversized pipes.
Ensures efficiency with minimal pressure loss.

Try the calculator above for your projects!

Check out 1 similar GPM to Pipe Size Calculator :

GPM to Pipe Size Calculator

Help Improve This Calculator

Your suggestions help us make better tools for everyone.