How to Measure for Gas Logs
Now let's take these measurements and use them to find the best gas logs for your fireplace.
Depth: For most gas logs, your fireplace needs to be a minimum of 12-14 inches deep.
Width: Your gas logs need a minimum of two inches of free space on both sides. To ensure this is the case, buy a set of logs (1) at least four inches shorter than the opening width and (2) no longer than the back width. Let's say your fireplace has a opening width of 28 and a back width of 22. (1) The logs at maximum will be 24 inches, but (2) they can't be longer than the back width so we'll go with a log size of 21 inches.
Height: Height is rarely an issue. If your fireplace is exceptionally short, you may want to look at the height of the gas logs, remembering that you'll need space for the flames above the log set.
Following these simple rules will ensure that your gas logs look beautiful and have the appropriate clearance for fire safety standards.