How to use this calculator
Enter the room in feet, count the doorways, and set the stock length you can get home. The plan draws the room from above with the trim run against each wall and the stock joints marked, so you can see which walls need a scarf joint before you start cutting.
Perimeter minus openings
The perimeter of a 12 by 14 room is 52 linear feet. That is the starting number and it is the only measurement most people take.
Then subtract what does not get baseboard. A standard interior door is 3 feet wide. Two doors removes 6 feet. A cased opening between two rooms might be 5 feet. A closet with bifold doors usually gets baseboard inside but not across the opening.
What you do not subtract: the width of a radiator, the space behind a fridge, or anything else that sits in front of the wall. Baseboard runs behind all of it, because the day the appliance moves you will see the gap.
Stock lengths and mitre waste
Primed MDF baseboard comes in 8, 12 and 16 foot sticks. Solid pine and poplar come in 8, 10, 12, 14 and 16. Longer is better and it is not close: a 15 foot wall run from a 16 foot stick is one clean piece, while the same wall from 8 foot stock is two pieces and a scarf joint in the middle that you will see under raking light for the rest of the time you own the house.
The 10% mitre allowance covers the length lost at each cut. A 45 degree mitre on a 5 1/4 inch tall baseboard eats about 5 inches of stick, and an outside corner eats it at both ends of both pieces. In a room with four inside corners and one outside corner, 10% is right. Add five points if the room has bay windows, columns or more than two outside corners.
| Stock length | Pieces | Total bought | Left over |
|---|---|---|---|
| 8 ft | 7 | 56 ft | 5.4 ft |
| 12 ft | 5 | 60 ft | 9.4 ft |
| 16 ft | 4 | 64 ft | 13.4 ft |
Longer stock costs more total length but fewer joints. Unless money is tight, buy the length that lets your longest walls run in one piece.
Inside vs outside corners
Inside corners should be coped, not mitred. A coped joint — one piece square to the wall, the other cut to the profile with a coping saw — stays tight when the framing moves. A mitred inside corner opens up the first winter and no amount of caulk hides it for long.
Outside corners are mitred, and they are where the waste comes from. Cut both pieces long, test the fit, then trim. Houses are rarely at 90 degrees: a corner at 91 needs two 45.5 degree cuts, and finding that angle takes a test piece.
Where a run ends in open air — beside a stair stringer, at a cased opening with no trim — you need a return: a small mitred offcut that turns the profile back into the wall. Two cuts on a scrap and it is the detail that separates finished work from unfinished.
Common mistakes
- Buying exactly the perimeter. Fifty-two feet of wall needs about 58 feet of stock. The mitres take the difference.
- Measuring the room, not the walls. Alcoves, chimney breasts and bump-outs each add two corners and several feet.
- Mitring inside corners. Cope them. It takes ten minutes to learn and it holds forever.
- Nailing into drywall only. Find the studs. Baseboard nailed to nothing pulls away from the wall the first time a vacuum hits it.
- Cutting every piece before fitting any. Measure, cut and fit one wall at a time. The method is set out in the baseboard and trim measuring guide.
- Painting after installation only. Prime and put the first coat on the sticks before they go up, then caulk and do one finish coat in place. Full method in how many coats of paint.