The best way to tell them apart is by their bill. If the bill is longer than the diameter of the birds head it is likely to be a hairy. A smaller bill is more likely to be a downy. The heavy bill of the hairy is more diagnostic than the size of the bird, although hairies tend to be larger. When you only see them one at a time, then larger bird, or smaller mean lacks meaning.
The best way to tell them apart is by their bill. If the bill is longer than the diameter of the birds head it is likely to be a hairy. A smaller bill is more likely to be a downy. The heavy bill of the hairy is more diagnostic than the size of the bird, although hairies tend to be larger. When you only see them one at a time, then larger bird, or smaller mean lacks meaning.
Ok thank you I looked it up and that was the first thing I read.