Built-in ovens come in three standard widths: 24, 27 and 30 inches. Those measurements can vary anywhere from 1 to 2 inches, and height and depth can also vary slightly. Double wall ovens have a greater height than single ovens.
Two built-in ovens may have the same dimensions, but the use of space inside the oven can vary. At about 3.5 cubic feet, wall ovens are already much smaller than the 5 cubic feet of the typical range oven. Check the interior measurements and use of space in wall ovens that fit the intended opening to maximize the available baking area.