What do the spf numbers on sunblock/sunscreen mean? how do i know what the right amount of spf is for me?

Sunprotection factor: Spf means sun protection factor and is a measure of the amount of protection from the sun a sunscreen provides. So the higher the spf the more protection it gives from the sun and the longer you can stay out after application. It is difficult to say exactly how long you can stay out based on the spf only as it depends on sun intensity. So the higher the spf the better generally speaking.

Anything over 30 is : Spf stands for sun protective factor. Spf 15 means it takes 15 x longer to burn. It is measured by the time it takes to turn red in uv light. Sunburn depends on the intensity of light & the type of skin. Since spf 30 blocks 97% of uv, higher # means little. Note that spf refers only to uvb, not uva. Also they all need to be reapplied every few hrs.