Hi Bev, that is a bit confusing! A lot will depend on how high rising your recipe is in the 9" X 9" pan. For a very high rising cake, you might be better off multiplying by 1.5, as Elisabeth suggests, but for most recipes we think multiplying the weight of each ingredient by 2.16 should work to convert from a 9" X 9" X 2" pan to a 13" X 18" X 1" pan. The way we got there: To go from a 9" X 9" to a 9" X 13" pan would require multiplying by 1.44. If you then multiply that by 1.5, that would get you to the half sheet pan size. 1.44 X 1.5 = 2.16. 

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