About the Door Casing Calculator
The Door Casing Calculator figures out how much interior trim you need to finish the openings around a set of doors, converting a door count into total linear feet of casing material. It is built for interior finish carpentry, not exterior door trim, and works whether you are trimming one new door or an entire house of rough openings. Because casing is sold in fixed-length sticks rather than by the foot, the tool also converts your linear footage into a shopping count of standard-length pieces.
How It Works
You enter the number of doors and whether both sides of each opening need casing (a passage door between two rooms) or just one side (a closet opening finished from a single face). The calculator assumes a fixed 17 linear feet of casing per side, covering two vertical legs and one head piece with allowance for the mitered corners, then multiplies by 1 or 2 sides accordingly. That total is divided by 7 feet, the length of a standard pre-cut casing stick, and rounded up to a whole number of sticks.
Formula & Methodology
To work this out by hand, first decide how many sides of each opening actually get trimmed. A hallway door between two finished rooms needs casing on both faces, while a single-sided closet opening might only need one. Multiply the door count by 17 feet for each side being trimmed, then divide the running total by 7 to find how many pre-cut sticks to buy, rounding any fraction up since lumber yards sell casing in whole sticks.
Examples
A Six-Door Interior Remodel
With the default entry of 6 doors and both sides selected, the calculator returns 204 linear feet of casing (6 x 17 x 2), which rounds up to 30 seven-foot sticks to buy.
Three One-Sided Closet Openings
For 3 doors with only one side trimmed, the total comes to 51 linear feet (3 x 17 x 1), requiring 8 seven-foot sticks after rounding up.
Advantages
- Converts an abstract door count directly into a stick count you can hand to a lumber yard or write on a purchase order.
- Accounts for the doubled material need of passage doors trimmed on both faces, a detail easy to overlook when estimating by eye.
- Gives an instant reorder reference when a mid-project miscut or design change requires buying a few more sticks.
Common Mistakes
- Forgetting that a passage door needs casing on both faces, which understates material needs by half on multi-room remodels.
- Buying exactly the calculated linear footage with no cushion for miter cuts, then running short by one stick near the end of the job.
- Applying the same 17 ft-per-side figure to oversized or double doors, which actually require more casing per opening than a standard single door.
Edge Cases to Watch For
- The 17 ft-per-side figure assumes a standard-height, standard-width residential door; taller openings or wide double doors need more material per side than this estimate provides.
- The calculator does not add a waste allowance for miscut miters or damaged pieces, so ordering one extra stick beyond the rounded-up total is common practice on real jobs.
- Unchecking the both-sides option cuts the total in half, which matters for closets, utility doors, or openings only trimmed from a hallway side.
Common Use Cases
- Homeowners planning a trim material budget before an interior remodel or new-construction finish carpentry phase.
- Contractors generating a quick casing material list for a bid without measuring every opening individually.
- DIYers replacing outdated trim throughout a house who need to know how many sticks to load into the truck.