Trim and Molding Calculator

Measure the total run, subtract anything not trimmed, add waste, then divide by the available length and round up. Buying by the metre without rounding leaves you a piece short.

More than the usual ten percent, sometimes a great deal more on a bold repeating profile, because each join has to align the pattern. The repeat length effectively becomes the minimum offcut.

A join cut at an angle rather than square, so the two pieces overlap. It hides a join in a long run far better than a butt joint, and it stays closed as timber moves.

It sits at an angle between wall and ceiling, so its cuts are compound rather than simple mitres. That makes it considerably less forgiving, and cutting it in the correct orientation in the saw is the usual difficulty.

Priming and a first coat before fitting is far easier than cutting in afterwards, leaving only filling and a final coat once installed. It is a substantial time saving on a large run.

Fix at high points and use flexible filler at the gaps, or scribe the back of the moulding to the wall profile. Forcing it flat against a bowed wall usually splits it at the fixings.

Either flat with compound angles, or nested in the saw at its spring angle with simple mitres. Nesting is easier to get right and limited by the saw's capacity for the moulding size.

One piece is cut square into the corner and the other is cut to the profile of the first with a coping saw. It handles out-of-square corners far better than a mitre and does not open as timber shrinks.

MDF is dimensionally stable, has no knots and takes paint beautifully; it swells irreversibly if it gets wet and holds fixings less well. For painted internal work it is usually the better choice.

The angle at which crown moulding sits against the wall, commonly 38 or 45 degrees. It determines the compound cuts, and mouldings with different spring angles cannot be mixed in one run.

A scarf joint cut at 45 degrees so the pieces overlap, positioned over a fixing point and away from the eye line. A square butt joint opens visibly as the timber moves.

Prime and give a first coat before fitting, then fill and finish once installed. It avoids cutting in around a complex profile against a finished wall.