This really depends on the individual usage including how often the devise is used and what power output it is set to. Under the Tobacco Products Directive (TPD), all E-Liquids must be manufactured in 10ml bottles in the UK. The average person uses a 10ml bottle in three days but this can vary considerably either way.
Coils and Clearomisers should last between one to four weeks depending on individual usage. The frequency can differ depending on the device used, amount it is used and the power output it is set to. If you feel you need to replace your Coil or Clearomiser too quickly, it may be an indication that you need to upgrade your device to something more suitable.
It is normal for your E-Liquid to taste burnt once your Coil or Clearomiser has worn out and needs to be replaced. This is not always apparent if you use your device set to a low power. We recommend replacing after a maximum of four weeks if you haven't experienced a burning taste for you to feel the full benefit of your devise.