The smallest woodpecker that is in North America is the downy woodpecker. Its name comes from the downy white feathers.
Their bill is about half the size of the hairy woodpeckers. Also, on the downy woodpecker’s white outer tail feathers they will have a few black bars. Hairy woodpecker outer tail feathers are all white. Downy woodpeckers are 6” and Hairy woodpeckers are 9 “in size. The males have red on nape, the females will have no red on their nape.
Downy Woodpecker, female is on the left side of the page and Hairy Woodpecker, male is on the right side of the page.