Window A/C Dimensions
The extra 4" on the window width requirement is from the expanding side panels, which, while expandable/collapsible, are likely a minimum of 2" wide each. If you're creative, you could use other means to close off the gap on either side of the unit (though with just a half inch on each side, you may not need to). I would check the return policy of wherever you choose to buy, though, in case it doesn't quite fit.