One 50ml bottle can be used -
1-2 times for long hair
3-4 times for medium hair
4-7 times for short hair
You get twice the amount of uses with the 100ml bottle size.
please note that the fuller(thicker) your hair is, the more color you would need, so you might get more or less uses from a bottle depending on your hair density and the type of outcome you want. This is just an estimate. for wigs/ longer hair lengths we advise getting the 100ml size