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 – 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.
Tips
- Use the figures printed on your product or its manual when you have them.
- Round quantities up so you are never short.
- Measure twice before you buy anything cut to size.
- Everything runs in your browser – try different values to compare options.
Common mistakes to avoid
- Mixing units (inches and centimetres, mAh and Ah).
- Ignoring efficiency losses and safety margins.
- Treating rules of thumb as exact.
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 borderGlass = opening + 2 × rabbet − fudgeOuter frame = opening + 2 × moulding widthMoulding length = 2 × (outer width + outer height) + waste for the four mitresWorked 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.
What formula does the Picture Frame Calculator use?
Opening = picture + 2 × mat border.