Rain Barrel Size Calculator
Estimate rainfall captured from a rectangular roof, target storage volume, full rain-barrel quantity, purchased capacity and barrel cost.
Default project preview
7 barrels
Event roof yield
673.2 gal
Target storage
336.6 gal
Purchased capacity
385 gal
Roof catchment area
1,200 ft²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Captured volume = roof area × rainfall depth × runoff coefficient. Target storage applies the selected percentage, then barrel quantity is rounded up.
FAQ
Rain Barrel Size Calculator questions
Why use a runoff coefficient below one?+
Some rainfall is lost to wetting, splash, debris, first flush and gutter inefficiency.
Can rain barrels prevent all stormwater runoff?+
Usually not. Once barrels fill, overflow must be routed safely away from foundations.
Is captured rainwater safe to drink?+
Not without an approved collection, treatment and monitoring system.