Sunscreen Calculator

Dermatological testing standards establish that effective sun protection requires a topical application rate of 2 milligrams per square centimeter of skin. To calculate your total need, the tool first determines your Body Surface Area (BSA) using the Mosteller formula: BSA = 0.007184 × Weight(kg)^0.425 × Height(cm)^0.725. From there, the base sunscreen volume for a full-body application is calculated in milliliters. Teaspoon measurements are derived using the standard conversion that 1 teaspoon equals approximately 5 milliliters. Specific anatomical zones—such as arms, legs, and the torso—are allocated proportional percentages of your total skin surface area to give you granular, easy-to-follow application guidelines.

Imagine an adult with a height of 175 cm and a weight of 70 kg going on a 7-day holiday, reapplying sunscreen every 2 hours during a 6-hour daily outdoor exposure window. First, their BSA calculates to approximately 1.83 square meters. Applying the 2 mg/cm² rule, their base full-body sunscreen requirement per application is roughly 36.6 grams (or milliliters). Since they reapply 3 times a day (6 hours divided by 2), their daily consumption is 109.8 mL. Over a 7-day holiday, this totals 768.6 mL of sunscreen. Dividing this by a standard 200 mL bottle volume yields about 3.84 bottles, which rounds up to 4 full bottles to ensure complete protection without running short.

Always apply your sunscreen 15 to 30 minutes before stepping outdoors so the protective film can properly bind to your stratum corneum. Do not forget commonly missed spots such as the tops of your feet, ears, back of your neck, and your lips. Finally, remember that standard sunscreen bottles lose their protective efficacy over time; always check expiration dates and replace your supply annually.