☀️ Sunscreen Amount Calculator
Based on the SPF-testing standard of 2mg per cm² for one full-body application.
Estimate how much sunscreen (in grams) is needed to cover your whole body at the labeled SPF, based on body surface area (Mosteller formula) and the widely-cited 2mg/cm² application density used in SPF testing. Most people apply noticeably less than this in practice.
How to use
- Enter your height (cm).
- Enter your weight (kg).
- The amount of sunscreen needed for one full-body application is calculated automatically.
How the calculation works
This tool estimates body surface area from height and weight and calculates how much sunscreen is needed to cover the whole body. Body surface area (m²) = √(height (cm) × weight (kg) ÷ 3600) (Mosteller formula) Amount needed (g) = surface area (cm²) × 2 mg ÷ 1000 SPF and PA ratings are measured with 2 mg of sunscreen per square centimetre of skin (ISO 24444 and similar standards), so you need that much to get the protection on the label. Most people apply half that or less, and with less product, protection falls well below the labelled SPF.
Worked example
Height 170 cm, weight 65 kg Surface area: √(170 × 65 ÷ 3600) ≈ 1.75 m² (17,500 cm²) Amount: 17,500 × 2 mg ≈ 35 g About 35 g for the whole body — roughly a shot glass. The face alone (about 3% of the body) needs about 1 g, around two pearl-sized drops.
Things to be aware of
- Sweat and towelling remove sunscreen. Reapply every 2–3 hours.
- The face, neck, ears and the backs of hands and feet are easy to miss.
- Skin covered by clothing does not need sunscreen, so scale the amount to the area exposed.
FAQ
What does "2mg per cm²" mean?
It's the standard application density used internationally when testing a sunscreen's SPF rating — applying this much achieves the labeled SPF protection. In practice people often apply less, which reduces the effective protection below the labeled SPF.
How is body surface area calculated?
Using the Mosteller formula (body surface area (m²) = √(height (cm) × weight (kg) ÷ 3600)), a formula widely used in medicine.
Can I find the amount needed for just my face?
This tool assumes full-body application. To estimate a specific area like the face, multiply by that area's rough share of total body surface area (the face is often estimated at around 3–3.5% of total).