Carpentry is a skilled trade and a craft in which the primary work performed is the cutting, shaping and installation of building materials during the construction of buildings, ships, timber bridges, concrete formwork, etc. Carpenters traditionally worked with natural wood and did the rougher work such as framing, but today many other materials are also used and sometimes the finer trades of joinery and cabinetmaking are considered carpentry. In the United States, there are about 1.3 million carpenters. The median annual wage for carpenters was $45,160 in May 2019. The top 10 percent earned more than $80,350, and the bottom 10 percent earned less than $28,470. Most carpenters learn their trade through a formal apprenticeship. Apprenticeships typically last 3 to 4 years. The first year is spent mostly in the classroom learning safety, blueprint reading, mathematics, and other basic skills. In the second and third years, apprentices do on-the-job training under the supervision of a journey-level carpenter. Carpentry is a physically demanding job that requires good health and stamina. Carpenters must be able to lift heavy materials and stand, stoop, kneel, and crouch for long periods of time.