How Much Baseboard Do I Need?

The easy number and the important one

The easy number is footage: perimeter, minus doorways, plus a bit for cuts.

The important one is whether each wall can be run in a single length — because a join in the middle of a wall is visible forever, and no amount of glue, filler and sanding makes it go away under raking light.

Most people work out the first and never think about the second until the trim is up.

The arithmetic

A room 14 by 12 feet with two 3-foot doorways.

Perimeter:

2 × (14 + 12) = 52 feet

Take out the doorways. Baseboard stops either side of an opening rather than crossing it:

52 − (2 × 3) = 46 feet of actual wall

Add waste at 10%:

46 × 1.1 = 50.6 feet

In 8-foot lengths:

50.6 ÷ 8 = 6.3, so 7 lengths

Why trim waste isn't like tile waste

With tile, waste is about area — the edges you cut off. With trim it's almost entirely about cuts, and specifically mitres.

Every mitred corner wastes a wedge. Every offcut under about a foot is unusable, because it's too short to span between studs and too short to look like anything but a patch. Those pieces accumulate fast in a room with several corners.

Ten percent covers a plain rectangular room. A room with an alcove, a bay window, a chimney breast or a lot of corners can easily want 15–20%.

Buy for the longest wall, not the total

This is the part worth changing your order for.

If your longest wall is 14 feet, then 8-foot lengths mean a join in it. Two joins, actually, since you'd need most of a second stick. Buy 16-foot lengths and that wall runs clean.

The trade-offs are real but small: longer sticks are awkward to carry, harder to get round a stair turn, and easier to bow while you're offering them up. Measure the route into the room before you order.

Total footage barely changes either way. What changes is how the finished room looks.

What comes out of the run, and what doesn't

Doorways come out. The trim stops at the casing on each side.

Windows don't. A window sits above the baseboard, so the run passes underneath it as normal.

Nothing else usually does. Baseboard runs behind furniture and across the back of alcoves. Only openings that reach the floor break the run — and if you're skipping the wall behind a fitted wardrobe, measure it out yourself rather than assuming.

Door casing isn't included. The baseboard butts into it, but casing is a different trim bought separately.

Cope the inside corners

The calculator doesn't care, but the job does.

A mitred inside corner looks perfect on the day and opens up as the timber moves with the seasons — you'll see a hairline shadow within a year. A coped joint, where one piece is cut to the profile of the other, hides that movement.

It takes longer and it's fiddly the first few times. It's also why professionals do it.

Let it acclimatise

Trim arrives from a warehouse at a different temperature and humidity to your house. Cut and fit it the same day and it'll shrink or swell afterwards, opening joints you just closed.

Leave it lying flat in the room for a few days first. Free, and it prevents the most annoying kind of callback.

Where people go wrong

• Not deducting doorways. Small per opening, and it's the easy one to catch.
• Deducting windows. They don't reach the floor.
• Buying the cheapest length. The join it forces is permanent.
• Ordering exactly. Offcuts under a foot are waste, not stock.
• Cutting the day it arrives. Let it settle.
• Not matching an existing profile. If you're adding to trim that's already there, take an offcut to the yard. Profiles vary more than you'd think.
• Forgetting the route. A 16-foot length has to physically get into the room.

The short version

2 × (length + width), minus the doorways, plus about 10% for mitres and short offcuts, divided by the stick length and rounded up. Then check your longest wall and buy a length that spans it — the footage is the easy part, and the single-piece wall is what you'll actually notice.