Hi, so there’s a few things to keep in mind when doing this, make sure to carry out a consultation and ask plenty of questions on the consultation etc.
Few things:
-the two methods can sometimes vary
-depending which make you use and weither is is single drawn(which would be thinner) or double drawn hair (which would look thicker right through to the ends)
-head space? Does you client have a small head or plenty of room?
-does your client have very thick hair(you will need 20/40g more than average)
-also it’s better if you client hasn’t a thick straight cut as it’s is hard to blend.
so I would advise (double drawn hair always)
80g-100g thickness only
120g-180g thickness and length
180-200g extra length and thickness
Again this is just my opinion and how I do things, you’ll learn as you get Experience and what works best for you
Hope it helps
