The amount of rainfall that you can collect is governed by the following formula:
Easy to Remember Formula: 1″ of rain x 1 sq. ft. = 0.623 gallons
To calculate the amount of rainwater you can collect, you need to know your annual average precipitation for your area. You can use the precipitation map below to find an approximate amount for your area.

Copyright: https://www.watercache.com/education/rainwater-harvesting-101 © 2021 Innovative Water Solutions LLC. All Rights Reserved.
Sitemap & Additional Resources: http://www.rwh.in/sitemap.htm .
Rainfall Data of US/UK/Australia
US : https://www.usclimatedata.com/
UK : https://www.metoffice.gov.uk/research/climate/maps-and-data
Australia : http://www.bom.gov.au/climate/cdo/about/cdo-rainfall-feature.shtml
Blog: https://rainwater.blog/ Last updated on 27-Mar-2023.