Roof Drain Sizing Calculator
Static · formula-only · worked example computed when this page was built · no live data
The Roof Drain Sizing Calculator picks the drain and leader size for a roof area at a design rainfall intensity. Example: for a 300 m² roof with 3 drains at 150 mm/h design rainfall, Drain size = 200 mm, Total flow = 12.5 L/s, Leader size = 200 mm (per IPC 2021 | Philippine Plumbing Code).
How it works
Computed from your inputs per IPC 2021 | Philippine Plumbing Code. Anything the worked example does not state uses this calculator's standard default; the interactive version shows every input and lets you change it.
Worked example (Plumbing & Pumps)
Inputs: a 300 m² roof with 3 drains at 150 mm/h design rainfall.
| Result | Value |
|---|---|
| Drain size | 200 mm |
| Total flow | 12.5 L/s |
| Leader size | 200 mm |
Computed by WorkHive's calculation engine when this page was built; standard: IPC 2021 | Philippine Plumbing Code.
How to use this calculator
- Read the worked example. It uses a 300 m² roof with 3 drains at 150 mm/h design rainfall and shows every number in the method.
- Follow the formula with your own figures: it returns Drain size, Total flow, Leader size, computed per IPC 2021 | Philippine Plumbing Code.
- To compute interactively, open the Roof Drain Sizing Calculator inside WorkHive's free Engineering Design suite (link below). It runs the same method with your inputs.
FAQ
What is a roof drain sizing calculator rainfall?
The Roof Drain Sizing Calculator is a free online tool that picks the drain and leader size for a roof area at a design rainfall intensity. It shows the formula and a fully worked example so you can check the method, not just the number.
How is it calculated?
The result is computed from your inputs following IPC 2021 | Philippine Plumbing Code. The worked example on this page shows a real computation with real numbers.
Is the calculator free?
Yes. WorkHive is free: this worked example is open to everyone, and the interactive calculator runs inside the free Engineering Design suite after a free sign-up (your work is saved to your account). WorkHive is a free, offline-first maintenance platform built for Philippine industrial plants.
Run it on your own numbers
Open the interactive Roof Drain Sizing Calculator in WorkHive. Free, and a free sign-up saves your calculations, BOMs and scope-of-works to your account.