We have a little over two acres, mostly wooded.  I bought this so we could use our deck at night without getting eaten alive by mosquitoes.  I placed it about 30 feet from our deck during a party last weekend.  Usually, around sunset, the Mosquitos come out and force us inside.  Not that night!  We had over 40 people outside, and not a single bite was reported.  I have to admit, both kids and adults enjoyed watching the bugs get zapped!  ;-). Highly recommended for any size yard!