Assessing the thickness of your natural eyelashes is essential before selecting eyelash extensions. It determines how much weight your natural lashes can support. The average natural lash thickness is 0.15mm. Eyelashes extensions range between 0.03-0.20mm in diameter. The safest thickness to go for is 0.05mm or 0.07mm. As of 2021, the most demanded thickness is 0.07mm.