Calculate two horizontal rails and two vertical rails with 45° miters and identical moulding profiles. All calculator measurements are in metres: divide millimetres by 1,000 before entering them. For example, 300 mm = 0.300 m.
Use the outside dimensions of the complete artwork, mat or glazing package that must fit inside the rear recess. Enter fitting clearance as the total extra dimension, applied once to both width and height; 0.002 m means 2 mm overall, or 1 mm at each side when centred.
Rabbet overlap here means the horizontal width of the moulding’s lip, measured from the front opening edge to the rear recess shoulder. It is not the rabbet depth or the actual amount of artwork concealed after clearance. Moulding width is the full face width from the front opening edge to the outside edge.
| Reference | Where to measure | Meaning |
|---|---|---|
| Long point to long point | Along the outermost longitudinal edge, between the two miter tips | Finished outside frame width or height |
| Short point to short point | Along the front opening edge, between its intersections with the miters | Visible front opening width or height |
| Rabbet reference | Along the rear recess shoulder, between its intersections with the miters | Package dimension plus total fitting clearance |
Let D be the package width or height, C the total fitting clearance, R the rabbet lip width and M the full moulding width. For each orientation:
- Rear rabbet opening B = D + C.
- Short-point length S = B − 2R.
- Long-point length L = S + 2M = D + C + 2(M − R).
At 45°, each transverse offset adds the same distance along the rail at each end. The long-point equation follows the frame-dimension rail formula published by Vermont Hardwoods; the short-point equation follows by subtracting twice the full moulding width. Clearance is included once per dimension.
The stock estimate uses P = 2L_width + 2L_height, separate kerf allowance K = 8k, and estimated stock T = P + K. This calculator assumes two independent end cuts for each of four rails. This eight-cut budgeting convention is an explicit calculator assumption, not a universal cutting layout.
Enter k as material lost along the length of the stock at each cut. It is not necessarily the blade’s nominal kerf measured perpendicular to the cut. For a flat 45° miter, the geometric longitudinal projection is blade kerf divided by cos(45°), approximately 1.4142 times the blade kerf. Measure the effective loss on a test piece where possible.
Kerf does not change finished rail lengths: keep the blade on the waste side of each finished mark. Add further stock for end squaring, defects, setup cuts, angled offcuts, matching grain and your actual cutting sequence. This estimate does not optimise nesting or guarantee that a particular board length will yield all four rails. Vermont Hardwoods likewise treats cutting loss separately and notes that end trimming requires additional material.
Numeric bounds are: package width and height 0.001–10 m; total clearance 0–0.020 m; rabbet lip width 0.0001–0.100 m; moulding width 0.0002–0.500 m; longitudinal kerf allowance 0–0.020 m. Input increments are 0.0001 m (0.1 mm). These are calculator limits, not recommendations for frame construction.
Also check these relationships before using the results: M > R, width + C > 2R, height + C > 2R, and R > C/2 so a centred package retains positive overlap beneath the lip. To retain overlap even if the package shifts through all the available clearance, use R > C and allow suitable support for the actual package.
The calculator cannot automatically enforce these relationships with its registered arithmetic operations. A displayed number does not establish that the geometry is valid. Reject zero or negative opening lengths and any inputs that fail the checks above.
Assumes square corners, flat 45° miters, straight stock and the same profile on all four rails. Rabbet depth, package thickness, structural strength, wood movement and nonrectangular or compound miters are outside its scope. Defaults illustrate the arithmetic; choose clearance and overlap for your materials and verify the fit before final cutting.
| Quantity | Rectangular frame | Square frame |
|---|---|---|
| Package width × height | 300 × 400 | 200 × 200 |
| Total clearance C | 2 | 1 |
| Rabbet lip width R | 6 | 5 |
| Full moulding width M | 40 | 25 |
| Longitudinal kerf allowance k per cut | 4.5 | 3 |
| Rear opening width × height | 302 × 402 | 201 × 201 |
| Horizontal short-point length | 302 − 12 = 290 | 201 − 10 = 191 |
| Vertical short-point length | 402 − 12 = 390 | 201 − 10 = 191 |
| Each horizontal long-point length; make 2 | 290 + 80 = 370 | 191 + 50 = 241 |
| Each vertical long-point length; make 2 | 390 + 80 = 470 | 191 + 50 = 241 |
| Sum of four finished long-point lengths | 2 × (370 + 470) = 1680 | 4 × 241 = 964 |
| Separate eight-cut kerf allowance | 8 × 4.5 = 36 | 8 × 3 = 24 |
| Finished lengths plus kerf; other waste excluded | 1716 | 988 |
Artwork creation is required before publication: no registered thumbnail asset was supplied. Create and register a 400 × 400 pixel WebP depicting the cheerful yellow five-point star mascot with hands, floating without separate legs or feet, beside a rectangular picture frame with long-point and short-point measurement guides. Use a white background with playful navy, blue and teal educational graphics. Inspect neighbouring tool thumbnails for style consistency, then insert the registered asset as the first image block.