Chair Rail Calculator: Feet, Pieces & Cost

How the chair rail calculator works

A chair rail, called a dado rail in the UK, is a horizontal moulding run round a room partway up the wall. This calculator turns the length of that run into a number of pieces to buy. It adds your wastage allowance to the run, divides by the length of one piece and rounds up.

With the US defaults, a 50 ft run plus 10% is 55 ft, and 55 ÷ 8 = 6.9, so 7 pieces of 8 ft moulding, $98 at $14 each. The metric default, 15 m plus 10% in 2.4 m lengths, is also 6.9, so 7 pieces, £84 at £12.

Measuring the run

The run isn't quite the room's perimeter. A chair rail stops at door casings, so take the width of each doorway, casing included, off the total. Windows depend on the sill height: where the rail passes below a window it runs straight through, but where it meets the window casing it stops there too, and that length comes off as well. The guide from Bob Vila recommends measuring the walls at the height the rail will actually sit, which catches anything in the way.

Take a room 12 ft by 13 ft with two doorways, each 3.5 ft across with its casing. The perimeter is 50 ft and the run is 50 − 7 = 43 ft. With 10% added that's 47.3 ft, or 5.9 lengths, so 6 pieces. In metric, a room 4 m by 3.5 m with one doorway of 1.05 m has a 13.95 m run, 15.35 m with the allowance, and needs 6.4, so 7 lengths of 2.4 m.

How much extra to allow

Every corner costs moulding. The same guide says to allow about 1 ft per wall for mitre cuts and mistakes. In the room above, that's 4 ft on 43 ft, which gives 47 ft and 5.9 pieces, the same answer as the 10% default. On a room with many short walls, bay windows or chimney breasts, each extra corner adds another cut, so raise the percentage.

Walls longer than one piece need a joint. The guide's method is two pieces cut at opposing 45° angles so they overlap, placed over a stud where the nails will hold. Inside corners are coped rather than mitred, and outside corners are mitred at 45°. Because of those joints, short offcuts rarely get used, which is why the calculator rounds up to whole pieces.

Check it wall by wall

On a small room, it's worth counting each wall, because offcuts only help if they fit somewhere else. In a 12 ft by 13 ft room with no doors and 8 ft lengths, each 13 ft wall takes a full length plus a 5 ft piece, and each 12 ft wall a full length plus a 4 ft piece. The two 4 ft pieces come out of one more length, and each 5 ft piece needs its own, so the count is 4 + 1 + 2 = 7 pieces, the same as the calculator gives for 50 ft at 10%.

The metric room works the same way. With 2.4 m lengths, the two 4 m walls each take a full length plus a 1.6 m piece, and the two 3.5 m walls a full length plus a 1.1 m piece. The 1.6 m pieces need a length each, while both 1.1 m pieces fit in one, so again 4 + 2 + 1 = 7, matching 15 m at 10%. Where the wall-by-wall count comes out higher, buy that number instead; it means the offcuts are too short to reuse.

Where to put it

Height mostly changes how the room looks rather than how much you buy; the run only changes if a window comes down to the height you choose. Moulding maker Metrie gives the common range as 32 to 36 in from the floor, with a rule of thumb of about a third of the wall height: around 32 in on an 8 ft wall. It notes that some prefer about a quarter of the height, and that rails can sit anywhere from 24 to 72 in. In metric, a third of a 2.4 m wall is 0.8 m and of a 2.7 m wall 0.9 m.

Bob Vila's guide suggests painting or papering the walls first and touching up afterwards, marking the studs, and drawing a level line round the room at rail height. In older houses with sloping floors, a rail that's perfectly level can look crooked against the skirting, so it may need to split the difference between the level line and a steady height off the floor.

Pick a moulding no thicker than the door and window casings where it meets them, so the rail finishes cleanly against the trim. Measure the pieces on offer too: moulding comes in several stock lengths, and entering the length you'll actually buy is what makes the count right.