Are you going to put the in your self? If so Try one of the big box stores. If you can buy one off the shelf they are reasonable. Ordering is another story. Replacement window companies like Window World do not sell just the window they want to install it too. They are are 300.00 installed. They are a nation wide company and have been around sense 1994. They have a good reputation in my area but check them out.

If the window has brick or stone in lieu of siding, simply measure the opening brick to brick in both directions. Measure top, middle and bottom (the smallest dimension is your dimension), ie. if it’s 36″ at the top, 36 1/4″ in the middle, and 36 3/8″ at the bottom, go with 36″. If your windows are standard size you can find replacemants at Home Depot or Lowe’s for $225 and down. If you are going to install it yourself, you will need to break out the old window if it’s brick facade, get spray adhesive in aerosal can, and spray the glass completely and put painter’s paper or plastic on the outside. This will minimize the glass going everywher when you break it. Replacement windows mount by screws through the side into the existing wood framing. Note that replacement windows come in different thicknesses. You need to get the 4′ thick windows if your working with brick facade. This will allow you to maintain the interior trim and finish, and overlap the old caulk line outside. All the info above was with the conditions of masonry outside and metal framed windows existing. If the existing window is wooden (an older home) it will be wider and taller then standard sizes, so the frame top, bottom and sides will stay, and the sashes and side tracks need to be removed, then take the measurements same as above.