Extended fly adds 8' length  to a normal size fly for your tent.  Provides a shaded and protected area to front of tent.

8X10 extended fly will have 2' extension to rear of tent and 8' extension to front.

8x10 will have 1 foot overhang on stove tent side and 3' overhang on other side.

8x10 extended fly is the same as a 10x12 extended fly, that is why there is additional extension to back and additional side overhang. 

There is no guarantee on extended flys in windy conditions.  There is no extended fly made that can withstand normal extended fly placement on a tent in windy condition. During windy conditions, take the extended fly down to prevent wind from getting under the fly.  Extended flys flapping in the wind will tear out the grommets and eventually tear the extended fly to shreds.