Storm Drain Calculator
The Storm Drain Calculator uses the Rational Method to find the design stormwater flow for a catchment. Example: for a 1 ha catchment (C = 0.7) at 150 mm/h, 10-year return, Design flow = 291.7 L/s, Runoff coefficient = 0.7, Time of concentration = 6.8 min (per DPWH Blue Book | Rational Method).
How it works
Computed from your inputs per DPWH Blue Book | Rational Method.
Worked example (Plumbing & Pumps)
Inputs: a 1 ha catchment (C = 0.7) at 150 mm/h, 10-year return.
| Result | Value |
|---|---|
| Design flow | 291.7 L/s |
| Runoff coefficient | 0.7 |
| Time of concentration | 6.8 min |
Computed live by WorkHive's calculation engine; standard: DPWH Blue Book | Rational Method.
How to use this calculator
- Enter the figures for the duty you are sizing: the worked example below uses a 1 ha catchment (C = 0.7) at 150 mm/h, 10-year return.
- The calculator returns Design flow, Runoff coefficient, Time of concentration, computed per DPWH Blue Book | Rational Method.
- Check the worked example to confirm the method matches how you would do it by hand, then run your own numbers in the interactive tool.
FAQ
What is a storm drain rational method calculator?
The Storm Drain Calculator is a free online tool that computes uses the Rational Method to find the design stormwater flow for a catchment. 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 DPWH Blue Book | Rational Method. The worked example on this page shows a real computation with real numbers.
Is the calculator free?
Yes. WorkHive's engineering calculators are free to use, no sign-up needed for the tools. WorkHive is a free, offline-first maintenance platform built for Philippine industrial plants.
Run it on your own numbers
Open the interactive Storm Drain Calculator in WorkHive: free, no sign-up needed for the calculators.