Rainwater Tank Sizing Calculator
Plan tank capacity based on roof collection area and expected usage.
Step 1: Units
Step 2
Enter project measurements
Use decimals if needed (e.g. 3.5).
How to use this calculator
Enter catchment area, rainfall assumptions, and demand targets.
What the math is doing
Capture ≈ area × rainfall depth (converted to volume).
Frequently asked questions
First flush?
Subtract diverted volume manually.
Runoff coeff?
This model assumes 100% of rain reaches tank opening—adjust mentally.
Codes?
Potable rainwater is heavily regulated.
Mosquitoes?
Screen all openings.