Ultrasonic Diffusers: For ultrasonic diffusers, which use water to disperse the oil, a common recommendation is 3-5 drops of essential oil per 100 ml of water. This ratio ensures a balanced and pleasant aroma without being overpowering. 

Nebulizing Diffusers: These diffusers use pure essential oil without water. Typically, 10-15 drops are sufficient to create a strong aroma, but you can adjust based on your preference. 

Small Rooms (up to 150 square feet): 3-5 drops should be adequate for small spaces like bathrooms or small bedrooms. 

Medium Rooms (150-300 square feet): 5-10 drops are recommended for medium-sized rooms such as living rooms or larger bedrooms. 

Large Rooms (300+ square feet): For larger spaces, you may need 10-15 drops or more, depending on how strong you want the scent to be. 

Scent Intensity: If you prefer a subtle scent, start with fewer drops and gradually add more until you reach the desired strength. For a stronger scent, particularly if you’re using the diffuser for therapeutic purposes like stress relief or respiratory support, you can use more drops. 

Potent Oils: Some essential oils, such as peppermint, eucalyptus, and clove, are particularly strong and may require fewer drops to achieve the desired effect. Lighter oils, like lavender or chamomile, might require more.