Baseboard & Trim Calculator
Gives you the linear feet and the actual boards to buy. Longer boards mean fewer joins on a wall, so the count changes with the length you pick.
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We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure the floor
Length and width give the perimeter, which is the run of wall the baseboard follows. Add a section for each rectangle in an L-shaped room.
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Take off the doorways
A standard doorway is about 3 ft with no baseboard across it. Wide archways, closets and fireplaces come off too — put their total width in the second box.
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Add waste for the mitres
Every inside and outside corner is a 45-degree cut that shortens the board. Ten per cent covers a plain room; go to 15 or 20 for lots of corners, a patterned profile that has to be matched, or stain-grade wood where a bad cut cannot be filled.
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Pick a length before you count
Longer boards mean fewer joins in the middle of a wall, which is the difference between trim that looks fitted and trim that looks patched. Measure your longest wall — if a 16 ft board covers it in one piece, that is worth the awkward journey home.
Boards by room size
One doorway deducted, 10% waste.
| Room size | Baseboard needed | 8 ft boards | 12 ft boards | 16 ft boards |
|---|---|---|---|---|
| 8 × 10 ft | 33 ft | 5 | 4 | 3 |
| 10 × 10 ft | 37 ft | 6 | 4 | 3 |
| 10 × 12 ft | 41 ft | 6 | 4 | 3 |
| 12 × 12 ft | 45 ft | 7 | 5 | 4 |
| 12 × 14 ft | 49 ft | 7 | 5 | 4 |
| 12 × 16 ft | 53 ft | 8 | 5 | 4 |
| 14 × 16 ft | 57 ft | 8 | 6 | 4 |
| 16 × 20 ft | 69 ft | 10 | 7 | 5 |
Buy the length that covers your longest wall in one piece wherever you can.
What else the job needs
| Item | How much | Note |
|---|---|---|
| Finish nails (2 in.) | About 1 per 16 in. of run | Into the studs, not just the drywall. |
| Caulk | 1 tube per 40–50 ft | For the top edge against the wall. |
| Wood filler | 1 small tub per room | Nail holes and miter gaps. |
| Quarter round | Same length as the baseboard | Only if you are covering a flooring expansion gap. |
Paint or stain the boards before fitting. Touching up on the wall is far slower than a clean coat on a bench.
How much baseboard for a 12x12 room?
A 12 × 12 ft room has a 48 ft perimeter. Take off 3 ft for one doorway and you need 45 linear feet. Add 10% for mitres and that is 50 ft to order — five 12 ft boards, or four 16 ft.
Why longer boards are worth the trouble
A join in the middle of a wall is called a scarf joint, and however carefully you cut it, it will show once the light rakes across it and the wood moves through a heating season. A wall covered by one board has no joint to open up.
Measure your longest wall before choosing. If it is 13 ft, a 16 ft board covers it whole and a 12 ft one does not — and that single decision matters more to the finished look than the profile you pick.
Inside corners: miter or cope?
Mitered inside corners open up as the house moves and the wood shrinks. A coped joint — where one board is cut square into the corner and the second is shaped to its profile — stays tight through that movement, which is why finish carpenters cope inside corners and miter only the outside ones.
Coping is slower and takes practice. For a painted room, mitres plus caulk are perfectly acceptable. For stain-grade wood, cope.
Do you need quarter round?
Only when you need to cover a gap. New floating floors need a 1/4 to 3/8 in. expansion gap at the wall, and quarter round or shoe molding is what hides it. If the baseboard is going on after carpet, or the floor is tight to the wall, you can skip it.
If you do use it, buy the same length as the baseboard — the run is identical.
Fitting to a floor that is not level
Old floors dip and new baseboard is dead straight, so you get a wedge of daylight under the board in the low spots.
Small gaps — under about 1/4 in. — disappear under quarter round or a bead of caulk. Larger ones need scribing: set the board in place, run a compass along the floor with the point following the floor and the pencil marking the board, then cut to the line. It takes a few minutes per board and it is the difference between trim that looks fitted and trim that looks bought.
Walls are rarely flat either. Where a board bows away from the wall, a screw into a stud pulls it back — countersink, fill, and it disappears.
Paint-grade or stain-grade?
This decides your waste allowance, your material and how fussy the job is.
Paint-grade — MDF or finger-jointed pine. Cheaper, perfectly straight, and caulk and filler hide every joint. Use 10% waste. MDF must never get wet, so keep it out of bathrooms and away from exterior doors.
Stain-grade — solid wood with visible grain. Every joint shows, so inside corners must be coped rather than mitered, and grain should be matched at joins. Use 15 to 20% waste, because a board with a knot in the wrong place becomes cut-offs.
For a first attempt at trim, paint-grade is far more forgiving and looks excellent when done carefully.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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perimeter = 2 × (length + width), summed over every sectionThe run of wall the baseboard follows. -
− (doorways × 3 ft) − other openingsNo baseboard crosses an opening. -
× (1 + waste ÷ 100)Mitered ends and mis-cuts. 10% plain, up to 20% for many corners. -
÷ board length, rounded upTrim is sold in whole lengths, not by the foot.
Common questions
How do I calculate linear feet of baseboard?
Add up the perimeter of the room, then subtract the width of every doorway and opening. That figure is your linear feet. Add 10% for mitres before you buy.
How much extra should I buy?
Ten per cent for a plain rectangular room, fifteen if there are several corners or the wood is stain-grade, twenty for a complicated profile that has to be pattern-matched at every join.
Should I buy 8, 12 or 16 foot boards?
The longest that covers your longest wall in one piece, and that you can actually get home. Joins in the middle of a wall always show eventually. Twelve feet is the usual compromise.
Do I subtract doorways?
Yes — about 3 ft for a standard door. Cased openings, closets and fireplaces come off too. Forgetting them means buying a board or two more than you need.
Should I paint before or after installing?
Before, on a bench, with the final coat touched up after the nail holes are filled. Painting trim in place is slow, and cutting in along a finished floor is the fiddliest part of the whole job.
What is the difference between mitring and coping?
A miter cuts both boards at 45 degrees to meet in the corner. A cope cuts one board square and shapes the second to fit against its profile. Coped inside corners stay tight when the house moves; mitered ones open up. Outside corners are always mitered.
How tall should the baseboard be?
Roughly proportional to the ceiling. Three to four inches suits an 8 ft ceiling, five to seven inches suits 9 or 10 ft. Taller trim in a low room makes the ceiling feel lower still.
Do I need quarter round as well?
Only to cover the expansion gap left by a floating floor. If the flooring is tight to the wall, or you are fitting baseboard over carpet, you do not need it.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- Architectural Woodwork Standards — trim grades and joint tolerances for paint- and stain-grade work
- Manufacturer profile data — stock lengths of 8, 12 and 16 ft for MDF and softwood trim
- NALFA installation guidance — the expansion gap that quarter round is there to cover
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 11, 2026.