UV Index in San Francisco Today
September 27, 2026 · San Francisco, USA
864,816 people
See today's UV index in San Francisco hour by hour below. The UV index shows how strong the sun's ultraviolet radiation is — the higher the number, the faster skin can burn. Values are calculated for San Francisco's coordinates and updated daily.
UV has dropped for today
Hour by hour
Clouds cut the peak by ~16%Protection windowClear sky
Remember today
- Sunscreen SPF 30+
- Sunglasses
Daylight: sunrise 07:02 – sunset 19:00
Tomorrow: UV 6 at its peak around 13:00
The UV index in San Francisco peaks at 5 (moderate) around 13:00 today. Sun protection is recommended between 10:39 and 15:30, while the index stays at 3 or above. Cloud cover is damping the peak by roughly 16% compared with a clear sky. Tomorrow the index is forecast to peak at 6 around 13:00.
UV index in San Francisco hour by hour
| Time | UV index | Level |
|---|---|---|
| 07:00 | 0 | Low |
| 08:00 | 0.2 | Low |
| 09:00 | 0.9 | Low |
| 10:00 | 2.1 | Low |
| 11:00 | 3.5 | Moderate |
| 12:00 | 4.6 | Moderate |
| 13:00 | 5.4 | Moderate |
| 14:00 | 5 | Moderate |
| 15:00 | 3.7 | Moderate |
| 16:00 | 2.3 | Low |
| 17:00 | 0.9 | Low |
| 18:00 | 0.2 | Low |
| 19:00 | 0 | Low |
UV index in San Francisco
San Francisco lies at 38°N. The midday sun reaches 50.5° above the horizon in San Francisco today, against a yearly ceiling of 75.7°. Elevation is what sets the ceiling for UV, and over San Francisco it is high enough for the index to reach very high values through the summer months. San Francisco is on the coast, where water and sand reflect UV back up at you and the sea breeze hides the heat that would otherwise send you into the shade.
What is the UV index?
The UV index is an international scale describing the strength of the sun's ultraviolet radiation at ground level. It starts at 0 and is effectively open-ended — at mid-latitudes it rarely exceeds 8, while in the tropics and high in the mountains it can pass 11. The higher the number, the less time it takes to get sunburnt.
The UV index depends mainly on how high the sun is in the sky. That is why it peaks around solar noon and is greatest in summer near the longest day of the year. Clouds, ozone, altitude and reflection from snow or water also affect the value.
The WHO UV scale
| UV index | Level | Recommendation |
|---|---|---|
| 0–2 | Low | No special protection needed. |
| 3–5 | Moderate | Use sunscreen (SPF 30+), seek shade around midday. |
| 6–7 | High | Sunscreen, hat and sunglasses. Avoid the sun 12:00–15:00. |
| 8–10 | Very high | Extra protection. Limit midday sun exposure. |
| 11+ | Extreme | Avoid the sun at midday. Full protection required. |