Casing is the trim that frames doors and windows. Ordering enough takes some care, because each piece is cut with miters at the corners, which use up more length than the opening, and because you need full-length pieces for the long legs.
Casing around a door
A door cased on one side needs two legs and one head. With mitered corners, each leg is about the door height plus one casing width, and the head is the door width plus two casing widths:
per door side = 2 × (height + casing width) + width + 2 × casing width
A 32 × 80 in door with 2¼ in casing: 2 × 82.25 + 36.5 = 201 in, about 16.8 ft per side, or 33.5 ft for both sides.
Interior doors are usually cased on both sides; exterior doors often only inside.
Casing around a window
A window with picture-frame casing on four sides needs two legs and two horizontal pieces:
per window = 2 × (height + 2 × casing width) + 2 × (width + 2 × casing width)
A 36 × 48 in window with 2¼ in casing: 2 × 52.5 + 2 × 40.5 = 186 in, or 15.5 ft. Windows with a stool and apron need a different calculation for the bottom.
Example
Eight interior doors cased on both sides and four windows: (8 × 2 × 201) + (4 × 186) = 3,960 in, or 330 ft. With 10% waste, buy about 363 ft, or 52 sticks of 7 ft.
Choosing the stick length
Casing is often sold in 7 ft, 8 ft and 14 or 16 ft lengths. A door leg of about 82 in fits a 7 ft stick, so 7 ft sticks are efficient for standard doors, while the short heads can come from offcuts of longer sticks. Taller doors need 8 ft sticks for the legs.
Waste and tips
- Allow 10% for straightforward jobs and 15% or more for beginners, complex profiles or wood that must match in grain.
- Leave a reveal of about 3/16 in between the jamb edge and the casing; it hides small irregularities.
- Cut a test miter on scrap, and glue the miters as well as nailing them so they stay closed.
- The calculator counts miter cuts so you can estimate the time: four per door side and eight per window.
Cost
Primed MDF or finger-jointed pine casing is cheap; solid hardwoods and wide profiles cost several times more per foot. Add nails, wood glue, caulk and paint.