Rain catchment sizer

Monthly rain off your roof against what you use, and the tank to bridge the gap. Learn the ideas behind it in Lesson 20: Project: my water budget.

Planning tool

Compare the rain your roof can catch each month with what you use, then find the storage that carries you through the driest stretch. This is the month-by-month balance many state rainwater manuals use.

Climate zoneNot sure? See Lesson 3. Data is a teaching approximation for one city per zone.

Roof footprint draining to tanks (sq ft)Measure the footprint, not the sloped surface.

Runoff coefficient (0 to 1)About 0.8 to 0.9 for metal, a bit lower for shingle.

Household use from the tank (gal/day)

Garden use in the growing season (gal/day)

First-flush diverter

A planning estimate, not a design. Take it to a qualified professional before you buy or build.