How many calories are in a slice of white bread?

How to get close to this number

Estimate through mass and composition. A slice of sandwich bread weighs about as much as a small egg, and bread is mostly starch, which carries four calories per gram. Multiply a plausible slice weight by that density and you land close. Foods made almost entirely of one macronutrient are the easiest of all to estimate this way.

The framing in the explanation is the useful correction: a slice looks trivial, but a sandwich uses two, and the bread alone then matches a side dish before anything is put between them. Single-unit calorie figures are systematically underweighted because people evaluate the unit rather than the serving they actually eat.

Bread varies more than most staples. Slice thickness alone can move this figure by half again, seeded and wholemeal loaves differ in composition, and artisan loaves are denser than industrial sandwich bread. The number here describes a standard supermarket slice from a national nutrition database, which is a reference point rather than a description of your loaf.