How can I make a selection exact size?

Hi When you select the rectangle Marquis tool there whoould be a tool settings palette at the top, just below the menus; where is says Style choose the drop down Fixed and type in what you want.
Basically the same for the Crop Tool.
At the top you should see Width and Height, along with resolution.
You don't have to set resolution unless you intend to change it.
thanks .

you can make a selection exact size according to what you want to do , and howmany people you need to do that thing ,

first : Press (Ctrl+R) rulers will appear second : you can measure Your SELECTION by the mouse arrow ِAccording to The rulers