Cologne = 1-3% fragrance and will last 2-3 hours.

Eau de Cologne = 3-5% fragrance and will last 2-3 hours.

Eau de Toilette = 5-7% fragrance and will last 2-4 hours.

Eau de Parfum = 12-18% fragrance and will last 4-6 hours.

Perfume = 15=30% fragrance and will last 6-8 hours or more.

Layering will NOT make the fragrance last longer.  It will just last as long as the longest item you put on (and be a lot more powerful). 

Perfume is oil based versus cologne and eau de toilette which are water and alcohol based.  That is why perfume lasts longer.  Oil clings to the skin better.  A few other things to remember, if you apply it to "hot" spots then it will also last longer (inside of the knees, elbows, wrists, back of the neck, cleavage).  Also, do not overdo it - your nose will acclimate long before others - many people keep re-applying thinking the fragrance is gone, but it is not.  Sprays are usually too much, if you use the spray then hold your wrist out from your body and spray it there.  Finally, keep it off of your clothes - it will stain them and not last as long!