What size is a shadow in the middle of the day?

That depends on how big the object is, the time of year, and the location you are. obviously, the size would make a difference, the season determines the tilt of the earth changing the shadow length. if you were in Africa at midday, your shadow would be short since the sun is directly overhead. if you were in Antarctica at noon, the sun would be lower to the ground thus creating a longer shadow.