What is the UV index and how is it calculated?

The ozone-oxygen cycle converts UV light into heat, which blocks UV rays from reaching the surface. Find out how the ozone-oxygen cycle blocks UV light.

Key Takeaways

  • The UV index provides a daily calculation of UV radiation exposure risk.
  • It is determined based on factors including the ozone layer thickness over your location, cloud cover, time of year and city elevation.
  • The index ranges from 0 (minimal risk) to 10 (maximal risk), guiding you on the necessary precautions for skin protection.

If you have read How Sunburns and Sun Tans Work, you know that your skin is sensitive to ultraviolet (UV) radiation. The UV index is a value calculated each day that helps you to know how much UV radiation will reach you if you go outside. By knowing the index value for the day, you can take appropriate precautions. These precautions help you avoid sunburn in the short term and skin cancer in the long term.

The UV index is calculated based on four factors:


  • The thickness of the ozone layer over your city (detected using satellites)
  • The cloud cover over your city (clouds block UV radiation to varying degrees)
  • The time of year (in winter, UV radiation is lower than in the summer because of the sun's angle)
  • The elevation of your city (higher elevations get more UV radiation)

The UV index value ranges between 0 and 10, with zero being minimal UV exposure risk and 10 being maximal UV exposure risk. This page lists the proper precautions to take for the different index values.

Here are some interesting links:


Frequently Asked Questions

How does the UV index affect daily activities?
The UV index informs individuals how to safely plan outdoor activities by indicating the level of sun protection needed to avoid skin damage from UV radiation.
What measures can be taken to protect against high UV index levels?
To protect against high UV index levels, individuals should wear sun-protective clothing, apply broad-spectrum sunscreen, seek shade during peak UV radiation hours, and wear sunglasses and hats.