How much hair would i need??

Hi there, me again lol

Thanks to all that have answered my previous questions am slowly
getting my head around everything!

Just wondering how much hair i would need to add about 5 inches onto
my own hair (my own hair length being at the top of my bra strap line)

Its all one length atm and im told i have quite alot of hair. Will be layering
it eventually, so will not need it to be really thick at the ends. How many
oz do you think i would need? Im thinking about 6-8oz? or would this not
be enough?

Thanks
Hayley :)