UV index in San Francisco in May
In May, the UV index in San Francisco typically peaks around 7.9 at midday — high on the WHO scale — with individual days reaching 8.4 in recent years. Sun protection is needed around the middle of the day.
How fast would you burn?
Estimated time to sunburn in unprotected midday sun at UV 7.9:
| Skin type | Time to burn |
|---|---|
| I — Very fair | ~17 min |
| II — Fair | ~21 min |
| III — Medium | ~30 min |
| IV — Olive | ~38 min |
Estimates from typical minimal erythemal doses — see methodology. Darker types (V–VI) burn slower still. Reflection off water or sand shortens all of these.
What to do about it
- SPF 30–50 every day, applied before you go out and reapplied every 2 hours.
- Plan beach, hiking, or long outdoor time before 11am or after 3pm when you can.
- A hat and sunglasses stop the exposure your sunscreen misses — face and eyes take the worst of it.
Planning a trip? Check the live UV index in San Francisco closer to your dates — day-to-day cloud cover moves the real number around this average.
San Francisco's UV year at a glance
| Month | Typical midday peak | Level |
|---|---|---|
| January | 2.9 | Low |
| February | 3.9 | Moderate |
| March | 5.5 | Moderate |
| April | 6.9 | High |
| May | 7.9 | High |
| June | 8.2 | Very high |
| July | 8.1 | Very high |
| August | 7.5 | High |
| September | 6.4 | High |
| October | 5 | Moderate |
| November | 3.3 | Moderate |
| December | 2.7 | Low |
The strongest month is June (typical peak 8.2); the gentlest is December (typical peak 2.7).
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