The amount of essential oil drops that you use in a diffuser will vary according to the size and make of machine you are using, the size of your space, and your personal tolerance for whatever scent you are diffusing. Always consult your manual for specific instructions. In general, you will use 3 to 5 drops in a 100ml oil diffuser, with some larger models that run for several hours using up to 20-25 drops. It’s always advisable to start with fewer drops and to work up from there.