Sunscreen Calculator

Sunscreen protects your skin from ultraviolet (UV) radiation, which is emitted by the sun. UV rays are divided into UVA and UVB types — both can cause skin damage, premature aging, and increase the risk of skin cancer. Regular sunscreen use significantly reduces these risks, especially during prolonged outdoor exposure.

Dermatologists generally recommend a broad-spectrum sunscreen with SPF 30 or higher, which blocks about 97% of UVB rays. SPF 50 offers slightly more protection at around 98%. For swimming or sweating, choose a water-resistant formula and always reapply every 2 hours regardless of the SPF level.

The standard recommendation is 2 mg of sunscreen per cm² of exposed skin. In practical terms, this works out to roughly 35 ml (about 7 teaspoons) to cover an average adult body in swimwear from head to toe. Most people apply far less than this, which significantly reduces the effective SPF protection received.

Multiply the amount needed per application by the number of applications per day, then by your trip duration. You need to reapply every 2 hours when outdoors, so a 6-hour beach day requires about 3–4 applications. Our calculator estimates your exposed skin area based on your height, weight, and clothing, then works out the total ml and number of bottles needed.

For an average adult in swimwear, a single application requires around 35 ml. So a 50 ml bottle covers roughly 1–2 full-body applications. If you're outside for 6 hours per day and reapply every 2 hours, a 50 ml bottle would barely last a single day for one person. Larger bottles are far more practical for trips.

For a week-long beach holiday with 6 hours of outdoor time per day, an average adult in swimwear needs approximately 700–1000 ml of sunscreen in total. That's roughly 4–7 standard 150 ml bottles. The exact number depends on your body size, clothing coverage, and how consistently you reapply.

No — SPF does not directly represent minutes of protection. SPF stands for Sun Protection Factor and indicates how much longer you can stay in the sun without burning compared to wearing no sunscreen. If your unprotected skin starts to burn in 2 minutes, SPF 30 theoretically extends that to 60 minutes. However, reapplying every 2 hours is still recommended regardless of SPF level.

Sunscreen should be reapplied every 2 hours when you are outdoors, or more frequently after swimming, sweating heavily, or toweling off. Water-resistant sunscreens maintain protection for 40–80 minutes in water, but should still be reapplied after drying off. Reapplication is essential even with high SPF products.