Simply measure your old doors and order the exact same size.
Follow instructions below to measure your new doors and drawer fronts.

Choose how much of the face frame the new door/drawer front will cover on each side (e.g., 1/2").
Measure the width and height of the cabinet opening the piece will cover.
Since the overlay applies to left + right and top + bottom, add twice the overlay to each dimension.
Finished Width = Opening Width + (2 x overlay)
Finished Height = Opening Height + (2 x overlay).
When centered over the opening, the piece will overlay the face frame by your chosen amount (1/2" in the example) all the way around.
If you change the overlay amount, make sure there's enough space between adjoining doors and drawer fronts so everything opens and closes smoothly.
Note: Double doors use a different calculation than the single-piece method above. (The steps here apply to single doors and drawer fronts.)
(W x H) ÷ 144