Determining a SPF Rating

The SPF of a sunscreen is based on scientific calculations that are rigorously performed in a laboratory.

The calculations of SPF are based on:

  • The amount of time it takes for skin to burn when in the sun.
    For example, if your skin burns after 10mins in the sun, a SPF 30 would allow 10x 30 mins of safe exposure in the sun without burning, 
  • However, the score is based on the correct amount of sunscreen being applied to all areas and not washed or rubbed off.
  • During laboratory tests sunscreen is applied liberally and the SPF rating is based on liberal application.
  • In the laboratory sunscreen is applied at 2mg/cm2.
    • This is equivalent to approximately 35mls if wearing a swimsuit.
    • For a 110ml bottle of sunscreen that is 3 applications!

In reality, people do not apply the same amount of sunscreen on their skin, as used in laboratories during testing!

  • Most people apply 0.5-1.5mg/cm2 which is equivalent to 25-75% of the recommended amount.
  • Application procedure can be poor at times with
    • Missed areas of sunscreen
    • Sunscreen being rubbed or washed off 

Protection Category

1998 Standard

2012 Standard


SPF 4 – 7

SPF 4, 6, 8, 10

Moderate (or medium)

SPF 8 – 14

SPF 15, 20, 25


SPF 15 – 29

SPF 30, 40, 50

Very high

SPF 30 or 30+

SPF 50+

Above is a chart on how SPF standards have changed since 1998.

Stay Up To Date

This information will not be passes on. This information is just used by Advanced Skin Academy to ensure you are kept up to date.