A framed picture usually sits behind a mat that overlaps the artwork by about ¼ in on each side. The frame’s rabbet (the lip that holds the glass) hides the edge of the glass and mat, so the glass is cut a little smaller than the rabbet size, by about ⅛ in, so it drops in easily.
How to use the Picture Frame Calculator
- Picture width
- Picture height
- Mat border width
- Moulding (frame) width
- Rabbet width
- Fudge allowance
- Waste for mitres
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the picture size, mat border width, moulding width, rabbet depth and fudge allowance.
Inputs explained
| Field | What to enter |
|---|---|
| Picture width | Units: in, cm |
| Picture height | Units: in, cm |
| Mat border width | Units: in, cm |
| Moulding (frame) width | Units: in, cm |
| Rabbet width | Units: in, cm |
| Fudge allowance | Units: in, mm |
| Waste for mitres | In % |
What each result means
- Mat outer width = [Picture width] + 2×[Mat border width]
- Mat outer height = [Picture height] + 2×[Mat border width]
- Glass width = [Mat outer width] – [Fudge allowance]
- Glass height = [Mat outer height] – [Fudge allowance]
- Outer frame width = [Mat outer width] + 2×([Moulding (frame) width] – [Rabbet width])
- Outer frame height = [Mat outer height] + 2×([Moulding (frame) width] – [Rabbet width])
- Moulding to buy = 2×([Outer frame width] + [Outer frame height])×(1 + [Waste for mitres]÷100)
Example values
How the main result changes when Picture width changes and everything else stays at the example values above:
| Picture width (in) | Moulding to buy (in) |
|---|---|
| 4 | 59.4 |
| 6 | 63.8 |
| 8 | 68.2 |
| 10 | 72.6 |
| 12 | 77 |
| 16 | 85.8 |
Formula
Opening = picture + 2 × mat border
Glass = opening + 2 × rabbet − fudge
Outer frame = opening + 2 × moulding width
Moulding length = 2 × (outer width + outer height) + waste for the four mitres
Worked example
Inputs: Picture width: 8 in; Picture height: 10 in; Mat border width: 2 in; Moulding (frame) width: 1.5 in; Rabbet width: 0.25 in; Fudge allowance: 0.125 in; Waste for mitres: 10 %.
Results: Mat outer width = 12 in; Mat outer height = 14 in; Glass width = 11.875 in; Glass height = 13.875 in; Outer frame width = 14.5 in; Outer frame height = 16.5 in; Moulding to buy = 68.2 in.
Frequently asked questions
How much moulding do I need for a frame?
The outer perimeter of the frame plus about 10% for the four 45° mitre cuts.
How much should a mat overlap the picture?
About ⅛–¼ in on each side so the artwork doesn't fall through.
What is a rabbet?
The recess on the back of a frame that holds the glass, mat and backing.