How the calculator estimates sunscreen amount
Dermatology and public-health guidance often describes a full-body adult application as about one ounce, or roughly 30 mL, for exposed skin. This calculator scales that rule to your body size using a standard body-surface-area estimate, then adjusts the amount by exposure level. Face-and-neck coverage needs far less product than beachwear-level full-body exposure, while larger body size usually increases the amount needed for even coverage.
The result is best understood as a practical planning target. Real use varies with product texture, missed spots, spray loss, thick versus thin application, and how much of the body is truly exposed. A calculator can estimate the right order of magnitude, but it cannot see how evenly the product is actually applied.