The average lot size is about .25 to about .33. Lots larger than that are nice but since the Borough is mostly built out (there are very few vacant lots left), you pretty much are limited to what's already here.
We are currently selling our home in Camp Hill and it is .63 acres, a few walking blocks from cedar cliff highschool and highland elementary. There are very few homes with a lot of .50 or greater. We love the large wooded lot our home sits on and it is big enough that we have a detached two car garage in the back also. We will be soon pulling it off the market to rent it because the current buyers seem to want a home with new everything and not pay for any of that. We have it priced at below it's fair market value to allow a new buyer to take out extra if they want different colored counters or paint or whatever but the home is move in ready.
Are you just looking for a vacant lot to purchase,? or are looking for a home sitting on a 1/4 acre or more lot? If you send me your wish list and what exactly you are looking for I'm sure I could find you something within the boro.