Picture Frame Molding Calculator
Enter one uninterrupted wall section to size equal molding boxes, list the miter cuts, and estimate how many stock pieces to buy.
Stock pieces to buy6
- Outside size of each frame
- 42 in (42.000 in) by 31 1/2 in (31.500 in)
- Inside opening of each frame
- 39 1/2 in (39.500 in) by 29 in (29.000 in)
- Miter cut list
- 6 horizontal pieces at 42 in (42.000 in); 6 vertical pieces at 31 1/2 in (31.500 in).
- Molding before waste
- 36.75
- Molding including waste
- 40.43
- Estimated molding cost
- $72.00
Cut lengths are measured outside long point to outside long point for 45-degree miters.
Stock-piece count is a linear-foot estimate and does not optimize offcut reuse.
How to use this calculator
- Measure the full uninterrupted wall width and the vertical area where the frames will sit.
- Choose the number of equal frames, side margins, gaps between frames, and top and bottom clearance.
- Enter the molding face width so the inside opening can be checked.
- Add the waste allowance, stock length, and price per piece to estimate the material order.
How the frame layout is calculated
This calculator treats one wall section as a row of equal rectangular frames. Measure around doors, windows, corners, built-ins, and other interruptions separately, because those breaks change the spacing and the cut list.
The outside width of each frame is found from the wall width left after the two end margins and the gaps between frames:
B = (W - 2S - (N - 1)G) / N
The outside height uses the available vertical area after the top and bottom margins:
H = A - 2V
- W is the wall width in inches.
- A is the available frame area height in inches.
- N is the number of frames.
- S is each side margin, G is the gap between frames, and V is each vertical margin.
The inside opening subtracts the molding face width from both sides of each dimension: inside width = B - 2M and inside height = H - 2M. The display rounds dimensions to the nearest 1/16 inch, but the linear footage and cost use the unrounded values.
How much molding to buy
Each rectangular frame needs two horizontal pieces and two vertical pieces. The cut list reports those as long-point lengths for 45-degree miters, so a frame count of N needs 2N horizontal cuts at B and 2N vertical cuts at H.
The total molding before waste is the perimeter of one frame multiplied by the number of frames:
L = 2N(B + H) / 12
Waste is then added with LA = L × (1 + P / 100). The stock-piece count is ceiling(LA / K), where K is the stock length in feet. Estimated molding cost is pieces × price per piece.
What changes the result most
Frame count, side margins, and gaps control the outside width. Vertical margin controls the outside height. Molding face width does not change the outside frame size, but it can make the inside opening too small, especially on narrow boxes or short rail-height layouts.
What this estimate leaves out
The stock count is a linear-foot estimate, not a cutting optimizer. It does not test whether every cut fits efficiently into the stock pieces, and it does not credit reusable offcuts from one wall against another wall. It also leaves out adhesive, nails, caulk, primer, paint, tax, tools, and labor.
Worked example
For a 144 inch wall with a 37.5 inch available frame area, three frames, 3 inch side margins, 6 inch gaps, and 3 inch top and bottom margins, each frame is 42 inches wide by 31 1/2 inches high on the outside.
With 1 1/4 inch molding, the inside opening is 39 1/2 inches by 29 inches. The cut list is six horizontal pieces at 42 inches and six vertical pieces at 31 1/2 inches. The total molding is 36.75 linear feet before waste and 40.425 linear feet with 10% waste. With 8 foot stock pieces at $12 each, buy 6 pieces for an estimated molding cost of $72.
Common questions
How do I calculate picture frame molding spacing?
Start with the uninterrupted wall width, subtract the left and right margins, then subtract the gaps between frames. Divide the remaining width by the number of frames to get each outside frame width. This calculator does that arithmetic and keeps the vertical spacing separate.
How many molding pieces do I need for box trim?
Each rectangular box uses two horizontal pieces and two vertical pieces. The calculator multiplies those cuts by the number of frames, adds your waste allowance to the total linear footage, then rounds up to whole stock pieces.
Should the gaps be equal on every side?
Equal gaps often look clean, but they are not required. Many walls use slightly different top, bottom, side, and between-frame spacing to align with outlets, rails, corners, or furniture. Keep the spacing consistent within one visible wall section when possible.
Are cut lengths measured to the long or short point of a miter?
This calculator reports each cut as the outside long-point length for 45-degree miters. That matches the outside frame dimensions shown in the result. Mark a test piece first if your molding profile or saw setup changes how you reference the cut.
How much extra molding should I buy for waste?
Ten percent is a common starting allowance for simple straight runs, but ornate profiles, many small frames, bowed stock, and first-time installation can need more. A zero waste allowance is allowed here, but it leaves no reserve for mistakes or unusable offcuts.
Can I use this calculator for wainscoting?
Yes, if the wainscoting uses rectangular applied molding boxes with equal spacing across one wall section. Calculate each uninterrupted section separately, and account for rails, stiles, panels, cap trim, or base trim outside this calculator.