Depends on the window. Cockpit windows have to withstand both dynamic and pressurization loads (at some point during the climb/descent in a pressurized aircraft, there is zero differential pressure between the inside and outside - I have no idea how to compute when). Dynamic loads must include protection from bird strikes. They are usually multi-layered laminated plastic/glass with a conductive for (electric) windshield heating. Most are around ¾ to 1 inch thick. By the way, heating a windshield is not just for deicing/ defogging, but to “soften” it (reduce brittleness) for bird strike protection. Many aircraft have, in addition to icing condition restrictions, lower speed restrictions when window heat is inop. For some more info, check out:
http://www.ppg.com/gls_ppgglass/aircraft/b757win3.htm
Passenger windows are much thinner (pressurization loads only). Warm air is routed between the inner and outer panes for defogging.
Early Learjets had acrylic windshields with external bleed air heating – and different Vmo’s for different altitudes. Around 300KIAS below 14,000’, 350+KIAS above 14,000 for bird strike protection. I wasn’t very comforted with these numbers when one day at 21,000 ft. a flock of Canada geese went OVER the airplane. Our ground school instructor was fond of saying that the “windshield was stressed for a four pound bird at 306 Knots or a 306 pound bird at 4 Knots”
Hope this helps.