SPF Calculator — Find Your Sunscreen
Enter your skin tone, today's UV index, and how long you'll be outside to get your personalised minimum SPF recommendation. All calculations run privately in your browser — no data is sent anywhere.
How the SPF Calculator Works
This SPF calculator combines two key variables to give you a personalised recommendation: your Fitzpatrick skin type and the local UV index. The Fitzpatrick scale classifies skin into six types based on how it responds to sun exposure. Type I (very fair) burns almost immediately and never tans, while Type VI (very dark) rarely burns and has the most natural melanin protection.
The UV index is a standardised scale that measures the intensity of ultraviolet radiation reaching the Earth's surface. A UV index of 1-2 is low (minimal risk), 3-5 is moderate, 6-7 is high, 8-10 is very high, and 11+ is extreme. The higher the UV index, the more protective SPF you need, and the more frequently you need to reapply. Check your local weather app or national meteorological service for today's UV index.
The calculator also accounts for your activity. Swimming and water sports wash off sunscreen faster — even water-resistant formulations are tested for only 40 or 80 minutes of water exposure. Outdoor sports that cause heavy sweating have a similar effect. The activity type adjusts your reapplication interval accordingly.
Understanding SPF Numbers
SPF 15 filters approximately 93% of UVB rays, SPF 30 filters 97%, and SPF 50 filters 98%. While the differences seem small in percentage terms, they matter significantly in practice: an SPF 30 allows twice as much UVB through compared to SPF 50. For most people in moderate to high UV conditions, dermatologists recommend SPF 30 as a minimum and SPF 50 or above when UV index is 6 or higher.
SPF only measures UVB protection — the rays that cause sunburn. For complete sun protection, look for a sunscreen labelled "broad-spectrum," which means it also protects against UVA rays. UVA rays penetrate deeper into the skin and are the primary driver of photoaging and skin cancer risk. In Australia and New Zealand, all sunscreens with SPF 15 or above must pass broad-spectrum tests. In the EU and UK, look for the UVA circle logo.
Sunscreen Tips for Maximum Protection
Apply sunscreen 15-20 minutes before going outdoors to allow it to bond with your skin. Most people apply far too little — the recommended amount for an adult is 2mg per square centimetre of skin, which works out to roughly one teaspoon for the face and neck, and about one shot glass (35ml) for the full body. Using less than this significantly reduces the effective SPF you get.
Even with high-SPF sunscreen, other protective measures improve overall sun safety: seek shade during peak UV hours (10am-4pm), wear a wide-brimmed hat, UV-protective sunglasses, and UPF-rated clothing when possible. Sunscreen is your last line of defence, not the only line. Reapplying is just as important as the initial application — set a timer based on this calculator's recommendation and stick to it.
SPF Recommendation by UV Index (Quick Reference)
Use this table as a quick reference when checking your local UV index. The values assume medium skin tone — go up one SPF level for fair/very fair skin, and you can stay at SPF 30 minimum for olive/dark/very dark skin even at lower UV.
- UV 1-2 (Low): SPF 15 minimum, especially for fair skin. Reapply every 2 hours.
- UV 3-5 (Moderate): SPF 30. Reapply every 2 hours; sooner if sweating.
- UV 6-7 (High): SPF 50. Limit midday sun (10am-4pm). Wear hat + sunglasses.
- UV 8-10 (Very High): SPF 50+. Seek shade. Reapply every 90 minutes outdoors.
- UV 11+ (Extreme): SPF 50+ plus protective clothing. Avoid prolonged sun exposure.
Updated 2026 Sunscreen Guidance
Recent dermatology consensus (AAD 2026 update) emphasises that broad-spectrum SPF 30+ is the minimum for daily use across all skin tones. New research has reinforced that mineral sunscreens (zinc oxide, titanium dioxide) and modern chemical filters approved in the EU and Australia (Tinosorb, Mexoryl) provide stronger UVA protection than older US-only formulations. If you're shopping for sunscreen in 2026, prioritise broad-spectrum, water-resistant, SPF 30 or higher, with the AAD or country-equivalent seal.
Last updated: May 2026. Sources: American Academy of Dermatology, WHO UV Index.
Frequently Asked Questions
What SPF do I need for UV index 8?
A UV index of 8 is classified as Very High. For most skin tones, SPF 50+ is recommended at UV index 8 or above. If you have very fair or fair skin, SPF 50+ is the minimum. For medium to olive skin tones, SPF 50 is appropriate, but SPF 50+ provides extra safety margin. Always reapply every 2 hours and more frequently if swimming or sweating.
Does dark skin need sunscreen?
Yes. While melanin does provide some natural protection — darker skin tones have a natural SPF equivalent of around 13 — this is not sufficient for prolonged sun exposure. UV radiation causes skin cancer across all skin tones, and darker skin is at increased risk of hyperpigmentation from UV damage. Dermatologists recommend a minimum SPF 30 for all skin types, including dark and very dark skin tones.
How often should I reapply sunscreen?
The general rule is every 2 hours when outdoors. If you are swimming or sweating heavily, reapply every 40-80 minutes, even if your sunscreen is labelled water-resistant. Water-resistant does not mean waterproof — it only means the product has been tested to retain protection for 40 or 80 minutes of water exposure. After that point, effectiveness decreases significantly.
What does the SPF number mean?
SPF stands for Sun Protection Factor. It measures how much UVB radiation is needed to cause a sunburn on protected skin compared to unprotected skin. SPF 15 blocks about 93% of UVB rays, SPF 30 blocks 97%, and SPF 50 blocks 98%. SPF 50+ is required in some countries (like Australia) to indicate very high protection. The SPF number does not indicate how long you can stay in the sun — it always needs to be reapplied every 2 hours.
Is SPF 50+ much better than SPF 50?
The difference is small in terms of UV ray blockage — SPF 50 blocks 98% of UVB, while SPF 100 blocks 99%. However, SPF 50+ formulations are often tested to higher standards in countries like Australia and Japan, meaning they may offer better broad-spectrum (UVA + UVB) protection. For everyday use, SPF 30-50 applied correctly is sufficient. The biggest factor is consistent and generous application, not chasing the highest SPF number.