Which weighs more a fully grown hummingbird or a pencil? While it is a well known fact that hummingbirds are very tiny, it may shock you to discover just how extremely tiny these birds actually are. A grown hummingbird weighs less then a pencil! That’s right, I said less then a pencil. The average hummingbird only weighs between 2 and 20 grams and that will depend on which species of hummingbird you are referring.