Estimate Roof Capture, Garden Demand, and Storage Before You Buy
Use your roof area, seasonal rainfall, expected capture losses, garden demand, and dry-period needs to see whether a proposed rainwater system fits your homestead.
This fill-in calculator separates water collection from storage so you can spot a rainfall shortfall, an undersized tank, or a design that is too difficult to maintain.
Start With the Two Numbers a Tank Cannot Fix
A larger tank cannot collect water that never reaches it, and a productive roof does not guarantee enough storage for a dry period. Check both sides before buying equipment.
| Quick check | Your entry |
|---|---|
| Usable roof catchment area | __________ |
| Seasonal rainfall | __________ |
| Expected capture-loss allowance | __________% |
| Proposed storage capacity | __________ |
| Dry-period garden demand | __________ |
First decision: If proposed storage is below dry-period demand, record the gap rather than assuming another heavy storm will solve it. If expected seasonal collection is below seasonal demand, a larger tank alone will not close that gap.
The complete calculator includes seasonal capture formulas, demand and storage comparisons, use-ranking fields, and maintenance and separation checks.