Start with the three specs that decide how a set looks and lasts: curl, thickness, and length. C curl gives a soft, natural lift and suits most clients; D curl reads more dramatic and holds better on straight or downward-growing lashes; L and L+ curls are made for hooded or deep-set eyes where a standard curl disappears behind the lid. For thickness, 0.15mm and 0.12mm work well for classic one-to-one sets, while 0.07mm, 0.05mm, and 0.03mm are built for volume and mega-volume fans that need to stay light on the natural lash.

Match length to what the natural lash can carry — usually no more than 2–3mm longer — and mix lengths across the eye rather than using a single size. Flat (ellipse) lashes are a good middle ground when you want a bolder line without added weight, and pre-made fans speed up volume work when hand-fanning slows a fill. Buying mixed-length trays first is the cheapest way to learn which sizes you actually reach for.