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Most people who use sunscreen don’t apply enough to get the protection claimed on the label. So how much sunscreen do we need?

It’s a good idea to apply the amount of sunscreen used to determine the product’s SPF value (SPF 15, SPF 30, SPF 50, etc.) on the SPF Test — a standardized test used by the FDA to determine how well a sunscreen protects skin from reddening when exposed to UV radiation. The test uses 2 milligrams of sunscreen for every 2 centimeters of skin.

Since bodies are different sizes and shapes, different people will need different amounts of sunscreen to reach 2 milligrams for every 2 centimeters of skin. We can measure the surface of our skin and do math (no thanks) or we can use general measurements that are probably good enough for most adults: apply 1/4 teaspoon of sunscreen to the face and 1/4 teaspoon to the neck, or 1/4 cup to your entire body (including your face and neck). Remember that larger bodies (more skin to cover) will need more sunscreen than smaller bodies. When in doubt, apply more, never less!