International Organisations have established the UV Index, which quantifies the intensity of the UVB radiation. The Index is measured at noon, according to the international procedure. Its values are divided according to the sun intensity:
Needless to say that not everybody has the same tolerance to sun exposure. Dark skins are more resistant than white ones and children's. That is the reason why it is necessary to take different kind of precautions, according to the UV Index and the type of skin. If you wish to find out your type of skin, click here.
In the following lines, you have posted a map of Spain with the daily UV Index of the most important cities. According to this index and type of skin, you will be able to take precautions to protect yourself.