A Weighted Average Source Distance (WASD) can be used to calculate food miles by combining information on the distances from production to point of sale and the amount of food product transported. The formula for the WASD is:

å (m(k) x d(k)) WASD = ————

å m(k) where:

k = different location points of the production

m = weight (amount) from each point of production, and

d = distance from each point of production to each point of use (or sale).

See Carlsson-Kanyama, Annika. 1997. Weighted average source points and distances for consumption origin-tools for environmental impact analysis. Ecological Economics, 23(1997): 15-23.