I've been researching this, and the best I can find (I have no evidence to support this, so use at your own risk) is between 360-400 calories per 100 grams. One source labeled it as 300 calories per cup.
I cannot say for all forms of Maltodextrin as their MacroNutrient Breakdown will be different in each product but the product I use is 190KCals per 50g which obviously puts it directly in the middle of the accepted answer.
28 grams is a oz-, a oz is 30cc's a tablespoon is 15cc and a teaspoon is 5cc, so 100 grams is about a 1/2 cup.
On Wiki 1gram is less than 4 cal.so that's close as you can get.
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