Rain Barrel Sizing Calculator

How It Works

Every 1 inch of rain falling on 1,000 sq ft of roof produces about 623 gallons of water. A typical 1,500 sq ft home collecting from half its roof can harvest 200+ gallons per inch of rain. Collection efficiency is about 80% after accounting for first flush diverters (which discard the first dirty water) and overflow. Standard 55-gallon rain barrels work for garden watering, but larger 275-gallon IBC totes or underground cisterns are needed for significant storage. Use a first flush diverter to improve water quality. Check local regulations — some areas restrict rainwater harvesting while others offer rebates.