Topsoil is the upper, outermost layer of soil, usually the top 2 inches (5.1 cm) to 8 inches (20 cm). It has the highest concentration of organic matter and microorganisms. Plants generally concentrate their roots in and obtain most of their nutrients from this layer. Just like we need to eat to maintain our health, soil needs continual replenishment of its organic matter to decompose into humus. Humus helps create a rich, moisture-retaining soil and makes nutrients available to plants.
A cubic yard of topsoil weighs approximately 2300 lbs = about 1.15 tons.