A quick reference

Body weight and body composition, side by side

MeasureBody weightBody composition
What it recordsA single total figure from a set of scalesThe proportion of fat, muscle, water and bone within that total
What it can missChanges in muscle or fat that offset one anotherDay-to-day fluctuation from hydration or food volume
Common way to track itBathroom scalesSkinfold callipers, tape measurements or bioelectrical devices
Typical use in this editorial contextA simple, low-cost starting pointA more detailed picture over weeks or months