It depends. What do you want your break out to be? I like 40-30-30 across the carb-protein-fat.
Here's one calc.
http://riverflag.com/nutrition/diabeticexchange.html
Fine tune it to wherever you need it to be. If you don't know your calorie level, get that here first.
http://www.freedieting.com/tools/calorie_calculator.htm
Then fiddle with the exchanges.
HTH!
A.