A form of estimation that is often, although not exclusively, used to size portfolio backlog items. T-shirt sizing is based on the concept of binning. The bins are typically assigned labels corresponding to those commonly used with T-shirt sizes: extra small, small, medium, large, extra large, etc. Frequently a cost range is associated with each size (e.g., an extra small project will cost between $10k and $25k) to provide organization-specific meaning to each T-shirt size. See also binning.