Picture Frame Size Calculator

Calculate picture frame moulding length from picture size, mat width, or outer frame dimensions, and get a 45° cut list in chosen units.

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Picture Frame Perimeter Formula

The perimeter of a rectangular frame is twice the sum of its outside height and outside width. The calculator uses three formulas depending on which measurements you have.

Picture + frame mode:

Outer frame mode:

Existing frame mat mode (perimeter plus visible mat):

• P = total moulding length (outside perimeter)
• H = picture height
• W = picture width
• m = visible mat width on each side
• f = moulding face width
• Ho = outside frame height
• Wo = outside frame width
• mat_tb = visible mat margin on top and bottom
• mat_lr = visible mat margin on left and right

Assumptions: the frame is rectangular with 45 degree miter joints, the moulding face width is uniform on all four sides, and the mat margins are equal on opposing sides. The calculator also reports a recommended purchase length of 1.10 × P to cover saw kerf, miter waste, and test cuts. The rabbet overlap in the existing frame mode adds to the visible opening to give the glass and backing size, since the rabbet hides a small lip of the glass behind the moulding.

The three modes match the three situations you usually face. Use Picture + frame when you start with a print and want to design the frame around it. Use Outer frame when you already know the finished outside dimensions and only need the perimeter. Use Existing frame mat when you have a frame in hand and need to figure out the mat opening and glass size for a specific picture.

Reference Tables

Standard print sizes and the moulding length you need with a 1 inch face frame and no mat:

Typical mat margins by picture size. Wider mats look more formal and give the eye room to rest:

Example and Common Questions

Worked example. You have an 11 × 14 print, want a 2 inch mat on every side, and chose a moulding with a 1.25 inch face. Outer height = 14 + 2(2) + 2(1.25) = 20.5 in. Outer width = 11 + 2(2) + 2(1.25) = 17.5 in. Perimeter = 2 × (20.5 + 17.5) = 76 in. Buy at least 76 × 1.10 ≈ 83.6 in, or about 7 ft of moulding.

Why add 10 percent for waste? Each miter cut removes a small wedge of stock, and the first cut on a fresh stick is rarely square. A 10 percent buffer covers the kerf on eight cuts plus one mistake on most jobs. For expensive hardwood moulding, bump it to 15 percent.

Should I measure the picture or the frame? If you are building a frame, measure the picture and the mat. If you are buying glass or backing for a frame you already own, measure the outside of the frame and the picture, then use the existing frame mat mode to back into the opening size.

What is the rabbet? The rabbet is the L-shaped lip on the inside back edge of the moulding that holds the glass, mat, picture, and backing. The rabbet overlaps the visible opening by about 1/8 to 3/8 inch on each side, so glass cut to the rabbet size is slightly larger than the visible opening.

How do the 45 degree cuts work? Each piece of moulding is cut with 45 degree miters at both ends. The long point to long point measurement on the outside of each piece equals the outer height or outer width of the finished frame. You need two pieces at the outer height and two pieces at the outer width.

Does this work for square frames? Yes. Enter the same value for height and width. The perimeter is simply 4 × side length.