Another question I get from clients, "how many bundles do you think I'd need?". 

The answer is based off two factors: 

Your head size & the length of hair you are interested in. 

Here is a chart on hair lengths in different patterns:

If you are not already familiar with hair extensions, I will simply tell you: 

The longer the hair length, the more bundles you'll need.

Some more key factors would be the look you are going for and how full you'd want your unit to be. 

Do not make the mistake of having a 20" - 21" head size, ordering 4 bundles of 12" straight hair for a blunt cut bob, but wanting a "natural & sleek look". 

In most cases, 3 bundles along with a lace closure is enough for a lace closure unit, that is if you are going for more of a natural looking custom unit of course. In other cases, you may be able to get away with just 2 bundles along with a lace closure. It all depends on the length of hair being used along with the look you are going for. For the fullness effect, 4 bundles along with a lace closure is recommended. 

If you have any further questions in regards to figuring out how many bundles to use, contact me, I'll be happy to assist.