What wind speed causes window glass to break?

It takes a lot for the average window to break. Traditionally architects and engineers will make sure that their glass is thick enough to withstand any speed of wind that nature can throw its way. For the most part, windows can break of the wind speed gets up to around 80 mph. Some thicker panes can withstand nearly 100 mph, but those are usually relatively rare and specialized for areas that will normally have higher winds.