1. Barn Owl (Tyto alba): Owlets are about 1-1.5 inches (2.5-4 centimeters) long and weigh less than 1 ounce (28 grams) at birth.
2. Great Horned Owl (Bubo virginianus): Owlets are around 2-3 inches (5-7.5 centimeters) long and weigh approximately 1-2 ounces (28-57 grams) when born.
3. Eastern Screech-Owl (Megascops asio): Owlets are roughly 1-1.5 inches (2.5-4 centimeters) long and weigh less than half an ounce (14 grams) at birth.
4. Barred Owl (Strix varia): Owlets are about 2-2.5 inches (5-6.5 centimeters) long and weigh around 1-1.5 ounces (28-42 grams) when born.
5. Burrowing Owl (Athene cunicularia): Owlets are approximately 1-1.5 inches (2.5-4 centimeters) long and weigh less than half an ounce (14 grams) at birth.
6. Northern Saw-whet Owl (Aegolius acadicus): Owlets are about 1-1.5 inches (2.5-4 centimeters) long and weigh less than half an ounce (14 grams) when born.
It is important to note that these are average sizes, and there can be some variation within each species. Additionally, owlets grow rapidly, so they quickly increase in size and weight in the days and weeks after hatching.