If you want to quantify protein and you have a spec:
1) Bradford Dye - pretty easy to do and cheap
some other ones - I've not used just done once a long time ago
2) Lowry assay
3) Smith assay
If you have a good spec - you would need it to have UV capabilities and a quartz curvette.
A280 = 1 A (mL/cm mg) x [Conc.] (mg/mL) x 1 (cm)
Using UV absorption can be tricky - has to be a pure sample (free from other UV absorbing substances) and different proteins will absorb differently. Some people use A205.
The Bradford assay is just using Coomassie Blue dye. It is okay but has problems with detergents and sometimes can be tricky due to the proteins. For example, one lab I was in used a animal protein for it's standard curve and we were testing for levels of a plant protein. That's not the best. For the best results, standard and test variable should be the same.
The Lowry and smith assays are both good, but a little time consuming to set up. I also think they are time dependant (can't remember ).