Rainfall Intensity Calculator Formula
Understand the math behind the rainfall intensity calculator. Each variable explained with a worked example.
Formulas Used
Rainfall Intensity
intensity_mmh = rainfall_depth / duration * 60Intensity
intensity_mms = rainfall_depth / duration / 60Variables
| Variable | Description | Default |
|---|---|---|
rainfall_depth | Total Rainfall Depth(mm) | 50 |
duration | Storm Duration(minutes) | 30 |
How It Works
Rainfall Intensity
Rainfall intensity is the rate of rainfall, critical for sizing stormwater drainage systems.
Formula
i = P / t
where P is the total depth of rainfall (mm) and t is the duration (hours). Shorter, more intense storms require higher drainage capacity. Design storms are typically characterised by intensity-duration-frequency (IDF) curves.
Worked Example
50 mm of rain over 30 minutes.
rainfall_depth = 50duration = 30
- 01Duration in hours = 30 / 60 = 0.5 h
- 02Intensity = 50 / 0.5 = 100 mm/h
- 03This is a relatively intense rainfall event.
Ready to run the numbers?
Open Rainfall Intensity Calculator