We are a desert climate and the sunniest city in Canada. I have 2 large rain barrels and it wasn’t enough.
Also, little rabbit hole if you want to go down. It’s not recommended to collect roof rain water (caveat, especially shingles 99% here), due to the chemicals in the tar, and for every roof, diseases from bird and rodent shit on the roof.
Fine for flowers and other stuff though.
This is why you always use the same tape measure. Tapes can measure differently, and some even need a set amount of tension to stretch it properly.