Two slices of rye bread contain 166 calories, and a 3-ounce serving of corned beef contains 213 calories. The butter used to grill the sandwich contains 36 calories per pat. Add a 1/2-cup serving of drained sauerkraut for 14 calories and a slice of Swiss cheese for 106 calories. Top the sandwich with 1 tablespoon of Thousand Island dressing for an additional 56 calories. Assembled, a homemade Reuben sandwich contains about 591 calories.