Baseboard & Trim Calculator
How many linear feet of baseboard, chair rail or crown molding do you need? Enter your room, subtract the doorways, and get the pieces to buy.
How to calculate how much baseboard you need
Baseboard is a linear problem, not an area problem — you are wrapping trim around the edge of the room, so what matters is the perimeter and where it stops, not the square footage. The honest way to count it:
- Add up the perimeter. Total the length of every wall getting trim. For a plain rectangular room that is 2 × (length + width); for an L-shaped or bumped-out room, measure and add each wall.
- Subtract the door openings. Baseboard and chair rail stop at every doorway, so take off the width of each opening. Do not subtract windows — the trim runs underneath them.
- Add waste for the corners. Every inside and outside corner is a mitered or coped cut, and some go wrong. Around 10% covers it for baseboard; use a bit more for crown.
- Convert to whole pieces. Molding is sold in fixed lengths (commonly 8, 12 or 16 ft). Divide your total by the stock length and round up.
Why the trim type changes the answer
The most common mistake is treating every kind of trim the same. Baseboard and chair rail run along the wall at floor and mid-height, so they are interrupted at each doorway — you subtract those openings. Crown molding runs where the wall meets the ceiling and passes straight over the top of every door, so nothing is subtracted and it needs a touch more waste because the corners are compound cuts. This calculator switches that behavior automatically when you pick the trim type, which is why a plain "perimeter" or area calculator quietly gives you the wrong number for doors.
How many pieces will I actually carry out of the store?
That depends on the stock length you buy. Suppose you need 42 ft of baseboard after waste. In 8-ft sticks that is 6 pieces (48 ft, so a little left over); in 16-ft lengths it is 3 pieces — fewer joints to fill, but harder to transport. Longer stock means fewer visible seams, so where you can, run each wall as a single piece and save the joints for the least visible spots. Our default assumes 8-ft stock; change it to match what your supplier carries.
What this calculator assumes
- Trim runs around the full perimeter you enter, minus door openings (for baseboard and chair rail).
- Windows and other above-floor openings are not subtracted.
- Default waste is 10% for baseboard and chair rail, 12% for crown molding; edit it for your job.
- Total is rounded up to whole stock pieces of the length you choose.
- Cost, if entered, is priced on the whole pieces you buy, not just the net length used.
Frequently asked questions
Do I subtract windows?
No. Baseboard passes under the wall below a window without stopping, so windows do not reduce the length. Only subtract openings that reach the floor and break the run — doorways, a fireplace hearth, or the face of built-in cabinets and closets.
How much extra should I buy?
The 10% waste built in covers mitered corners and normal mistakes. If the room has many corners, out-of-square walls, or an expensive hardwood profile you can't easily re-buy, bump the waste to 15%. It is cheaper to return one piece than to make a second trip for a single length that won't match.
Does this work for quarter round and shoe molding?
Yes — quarter round, shoe, chair rail and picture rail are all linear trims that follow the perimeter, so use the baseboard or chair-rail setting (they subtract doorways the same way). For crown, cove and other ceiling trims, use the crown setting so doorways are not subtracted.
How do I handle an L-shaped or irregular room?
Switch to "By total length" and add up every wall segment yourself, then enter the sum. The dimensions mode only fits a simple rectangle; for anything else, measure each wall and total them.