How much sunscreen should you use? The shot-glass rule, explained

Most sunscreen instructions say to apply generously. The familiar shot-glass comparison is a practical reminder of the amount used in FDA guidance for covering an average adult’s exposed body skin.

The one-ounce reference is for the body

The FDA says an average-sized adult or child needs at least one ounce—about the amount that fills a shot glass—to evenly cover the body from head to toe. This is a whole-body reference, not an amount for the face alone. Coverage needs vary with body size, clothing, and how much skin is exposed.

Sunscreens are tested using a specified amount. Applying a thin layer can make it harder to achieve the level of protection represented by the label. Use enough to cover the face and body as directed; real-world use can differ from standardized testing if the layer is sparse or uneven.

Work methodically, not by guessing

For body application, begin with an amount that reflects the one-ounce guidance, then cover exposed skin evenly. Pay attention to ears, nose, back of neck, hands, tops of feet, hairline, and exposed scalp. For lips, use a lip product labeled with SPF and follow its directions rather than assuming a general body sunscreen is appropriate there.

For the face, use the product’s directions and cover exposed skin evenly, including the hairline and ears. Avoid the eyes and mouth unless directions say otherwise. FDA says spray sunscreen should not be applied directly to the face.

Coverage is a routine, not a one-time number

The shot-glass comparison is not a substitute for the product label or a precise measurement for every body. It is a useful cue to avoid the tiny dab that leaves large areas thinly covered. Reapply as directed, at least every two hours when outdoors and sooner after swimming or sweating.

AREV Daily UV Fluid is in development. Final formula and SPF will be announced after finished-product testing. This article is general sunscreen education, not a claim about our product.

Sources

FDA: Sunscreen guidance and how to apply — https://www.fda.gov/drugs/understanding-over-counter-medicines/sunscreen-how-help-protect-your-skin-sun

AAD: How to apply sunscreen — https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/how-to-apply-sunscreen

FDA: Sunscreen labeling and effectiveness testing guide — https://www.fda.gov/regulatory-information/search-fda-guidance-documents/labeling-and-effectiveness-testing-sunscreen-drug-products-over-counter-human-use-small-entity