How long a wax melt should last is dependent on several factors.
In short, a good quality soy wax melt should provide around 8-12 hours of scent; this is on the basis that the wax melt is being used correctly. The wax melt will be ready to replace when it is no longer scenting your space.
There are several contributing factors that will either shorten or lengthen the life of your wax melt.
The size of your tealight
We only ever advise using a small, 4 hour tealight so that the heat emitted and distance between the flame and the well of the burner are safe.
A deeper tealight (typically 8 hour tealights), will heat the wax melt up too quickly and burn off the fragrance in less time. Not only will an 8 hour tealight burn off the fragrance too quickly, but it could cause your burner to overheat and subsequently crack.
The height of your burner (tealight not electric)
The shorter the burner, the closer the wax melt dish will sit above the tealight, causing the temperature of the melt pool to increase. The higher the temperature, the more the fragrance is burned off. This will cause you to experience a stronger, although shorter-lasting scent throw.
Smaller wax melt burners may mean that your wax melt lasts 8-10 hours, rather than 10-12 hours. With that being said, there should only ever be a small variation of height between different burner designs, as anything too short will be inappropriate for use with a tealight.
Electric wax melt burners will likely make the wax melt last the longest amount of time, when compared to a tealight burner. The potential downside to this is that the scent throw of the wax melt will be less than what it would be with a tealight burner. This is purely down to the temperature and whether you use an electric burner or tealight burner is entirely down to preference.
The quality of the wax melt you're using
The quality of the wax melt you're using is obviously a big factor. When launching a new scent into the Glass & Wick Soy Wax Melt collection, we always ensure a burn time of approximately 10 hours. If you want to understand more about what contributes to the best wax melts, you can read our thoughts here
You can also explore our entire collection of hand poured Soy Wax Melts here