Measure more than once. When measuring anything like a window, it's a good idea to measure twice, or even three times to be sure. The old adage, "measure twice, cut once" is very true and by only measuring once, you'll end up with some mistakes that could result in windows that don't fit properly.
Use a measuring tape. A yardstick or ruler will force you to guesstimate and that isn't accurate enough for ordering replacement windows. These measurements need to be quite accurate, so take the time to use the right equipment for the job.
Write it all down. It's easy to forget numbers, so either have a pen and paper handy or call out the numbers clearly for someone else to write them down. Do this for each of your measurements, to be sure they are the same.
Measure all sides. You might be tempted to just measure the top and side of a window, but in older homes particularly, the windows aren't always square. That means the varying sides of the window could be different in length, so be sure to check. Also, don't assume that all windows are the same size .. . measure each one separately. Make sure you number them, such as "Living Room Window 1", etc. to make it easy to identify the replacement windows when they arrive.
Make a map. It's going to be a lot easier to match the windows with their locations if you make a quick sketch of where each one is, label it and add the measurements, as well. You can refer to this when making your order and also when replacing the window.
How to Measure
Each manufacturer will provide you with instructions on how to measure the windows, but here are the basics for your own use. The instructions given here are for the traditional double hung window, but the procedure for other windows will essentially be the same.
For width, raise the sash and measure the lower part of the window from jamb to jamb at the top, bottom and middle to make sure you get accurate measurements. This must be repeated for each window that you are ordering replacements for.
In order to measure the height, stretch the tape measure from the jamb at the top of the window to where the sloped sill meets the inner window stool. Again, it's a good idea to measure in three places for this. With all your measurements, if the width or height differs in the three locations, use the smallest measurement to send to the manufacturer.
These replacement windows are usually built in quarter inch increments, making them quite precise in size. This means that it is vital to measure and then measure again with your old windows to be sure that you aren't going to end up with windows that don't fit. It's best to have them slightly smaller, since it's possible to fit smaller windows in and still have them work. However, an accurate measurement to begin with is a big help.
Replacing older windows can be done by the homeowner as long as the measurements are accurate. The map of which window goes where will really help when ensuring that they are being placed correctly.
