Soakwell Volume Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
100% FreeRuns in your browserBasic
Enter Values
Enter your values and press Calculate to see results.
How to use this calculator
- Enter the roof/catchment area (m²) and the rainfall event (mm).
- Read the litres to capture.
How it works
1 mm of rain on 1 m² is 1 litre, so litres = area × rainfall in mm.
Worked example
100 m² roof, 30 mm rain. = 3000 litres.
Common mistakes
- Using plan area vs actual catchment — use the roof's footprint area.
- Sizing to average rain instead of your local design storm.
Frequently asked questions
What rainfall figure should I use?
Use your council's design rainfall intensity for the storm event you must cater for, not a typical day.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.