Picture Frame Molding Length Calculator
Find the total length of molding to buy for a picture frame, allowing for the rabbet, mitre corners and cutting waste.
How it works
Opening = art + 2 × rabbet gap · Rail outer = opening + 2 × molding width · Perimeter = 2(long) + 2(short) · Total = perimeter + cut waste
A picture frame is four mitred rails, and each rail's outer edge is longer than the opening by the molding's face width at both mitred ends — the 45° cut adds a triangle of material equal to the profile width at each corner. The rabbet is the lip the artwork rests in, so the opening is cut slightly larger than the art to let it sit freely without buckling. Summing the four outer lengths gives the raw stick length, and the mitre saw turns some of it to sawdust, so a waste allowance per cut keeps you from buying one inch short.
Worked example
For 16 × 20 in art with a 1.5 in molding and a 1/8 in rabbet gap per side, the opening is 16.25 × 20.25 in. Each short rail is 16.25 + 3 = 19.25 in and each long rail 20.25 + 3 = 23.25 in, so the perimeter is 2(19.25) + 2(23.25) = 85 in. Adding 8 × 0.25 in of cut waste gives 87 in, about 7.25 ft.
Frequently asked questions
Why is the molding longer than the artwork perimeter?
The 45° mitre at each corner adds a wedge of material equal to the molding's face width. Wider profiles need proportionally more length, which is why a chunky frame consumes far more stick than a thin one for the same picture.
What is the rabbet gap for?
It is the small extra opening beyond the artwork size so the piece, glass and backing drop in without binding. About 1/8 in per side is typical; too tight and the art buckles, too loose and it rattles.
How much waste should I allow?
Each mitre cut loses the saw kerf plus a little for setup. Allowing 1/4 in per cut, and buying a single stick a few inches long, avoids being caught short on the final corner.
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This calculator is for educational purposes. Double-check important results before acting on them.