Pipe Capacity Calculator
Reference page for estimating gravity pipe capacity, velocity, and basic storm drain conveyance using open-channel assumptions.
Typical pipe capacity inputs
| Input | Why it matters |
|---|---|
| Diameter or pipe shape | Controls flow area and hydraulic radius. |
| Slope | Higher slope generally increases capacity and velocity. |
| Manning’s n | Represents pipe material, roughness, joints, and condition. |
| Flow depth | Partial-full pipes require more detailed geometry than full-flow estimates. |
| Tailwater and controls | May reduce capacity or change the hydraulic grade line. |
Screening workflow
- Confirm the pipe size, material, and slope.
- Estimate capacity using Manning’s equation.
- Check velocity for sedimentation and erosion concerns.
- Review inlet, outlet, junction, tailwater, and surcharge conditions.
- Use detailed hydraulic modeling where backwater or pressure flow may occur.