Compare two-slice sandwiches when bread slices weigh differently
Use slice weights to separate nutrient concentration from the total contributed by two slices in each sandwich.
Two slices of one loaf can weigh considerably more than two slices of another. A “per slice” comparison may therefore answer a different question from a “per 100 g” comparison. For a sandwich, it is useful to retain both views.
The FDA serving-size guidance describes household measures alongside their metric quantities. A slice count is useful context, but the associated weight makes the numerical comparison traceable.
Make the counted comparison first
Suppose fictional bread A declares one 30 g slice with 3 g protein and 150 mg sodium. Bread B declares one 45 g slice with 4.5 g protein and 180 mg sodium. Two stated slices of A provide 6 g protein and 300 mg sodium at 60 g total bread weight.
Two stated slices of B provide 9 g protein and 360 mg sodium at 90 g total bread weight. These totals describe the bread component of the two sandwiches. They do not include spreads or fillings.
Then ask the equal-weight question
Per 100 g, A has 10 g protein and 500 mg sodium. B has 10 g protein and 400 mg sodium. Their calculated protein concentration is equal, while B's calculated sodium concentration is lower.
Nevertheless, the larger two-slice portion of B contributes more sodium in this example: 360 mg compared with 300 mg. Neither calculation contradicts the other. One fixes the number of slices; the other fixes food weight.
Use actual slice weights when needed
Imagine two slices from A weigh 27 g and 33 g. Their combined 60 g matches two stated servings even though the individual slices differ. Weighing them together is enough for the sandwich total. If they instead total 66 g, the sodium estimate becomes 150 × 66 ÷ 30 = 330 mg.
This assumes the selected bread is reasonably represented by the package's average values. End slices, added seeds, and uneven coatings can introduce variation that a kitchen scale cannot fully characterize.
Save the result as either “two stated slices” or “two weighed slices,” not simply “two slices” if that distinction matters. Keeping portion and concentration columns separate lets you compare sandwich recipes without quietly changing the question whenever a loaf has thicker cuts.