How To Measure
For A Prehung Door

Four numbers — width, height, jamb depth and handing — decide whether a door fits. Ten minutes with a tape measure and this page gets all four right.

Every interior door quote comes down to slab width, slab height, jamb depth and handing. Get those four right and the unit fits. Here is how to find each one on a new opening or an existing door.

Existing door: open it and measure the slab itself, edge to edge and top to bottom. Do not include the jamb or the stop. Standard interior widths are 2-0 (24"), 2-4 (28"), 2-6 (30"), 2-8 (32"), 2-10 (34") and 3-0 (36"); standard height is 6-8 (80"). If you measure 29-3/4" wide, that is a 2-6 door that was trimmed — order a 2-6.

New rough opening: the framed hole should be 2 inches wider and 2 to 2-1/2 inches taller than the slab. A 2-6 × 6-8 door wants a rough opening of about 32" × 82-1/2". Measure the rough opening at top, middle and bottom and use the smallest width.

Door size	Slab width	Rough opening (width × height)
2-0 × 6-8	24"	26" × 82-1/2"
2-4 × 6-8	28"	30" × 82-1/2"
2-6 × 6-8	30"	32" × 82-1/2"
2-8 × 6-8	32"	34" × 82-1/2"
2-10 × 6-8	34"	36" × 82-1/2"
3-0 × 6-8	36"	38" × 82-1/2"

Measure the finished wall from drywall face to drywall face at the opening. A 2×4 wall with 1/2" drywall on both sides is 4-1/2", and our stocked 4-5/8" jamb covers it. A 2×6 wall measures 6-1/2" and needs a 6-9/16" jamb. Plaster, furring strips and tile returns all add thickness — measure, do not assume.

Stand in the doorway so the door swings away from you. If the hinges are on your left, it is a left-hand door; hinges on your right, right-hand. That is the whole rule. Bedrooms and baths usually swing into the room, so stand in the hallway.

Interior doors are not reversible once hung, and a wrong-handed unit is the most common reason a delivery goes back on the truck. When in doubt, send the desk a photo from the hallway side.

• Core: hollow or solid. See the core guide.
• Casing: WM473 colonial (stocked) or S4S flat.
• Lock bore: standard 2-1/8" bore, 2-3/8" backset unless you say otherwise.
• Floor: tile going in later? Tell us and we will leave the jamb legs long so the unit can be cut to the finished floor.
• Quantity and delivery address.

Exterior units add sill, threshold and buck to the equation, and impact-rated doors must be installed to the approved anchoring schedule. Measure the rough opening the same way, note the buck material (wood or concrete) and the sill condition, and let the desk size the unit. Read the Florida impact-door guide before you order.