Complete Guide to Picture Frame Dimensions
Getting picture frame dimensions right is one of the most important parts of presenting and protecting artwork. Whether you are framing a family photo, a fine-art print, a poster, a certificate, or a gallery piece, correct measurements help you avoid costly recuts, uneven borders, and fit problems. This page gives you a practical calculator and a complete reference so you can confidently order or build frames that fit the first time.
Essential Framing Terms You Need to Know
Before calculating, it helps to understand the core terms used by framers and frame suppliers:
- Artwork size: The exact width and height of your image, print, photo, or document.
- Mat border: The visible mat width around your artwork. A larger border creates more visual breathing room.
- Mat opening: The inner window cut from the mat. It is usually slightly smaller than artwork size so the mat can hold the piece in place.
- Mat overlap: The amount of art hidden under the mat, often around 1/8 inch per side.
- Package size: Total size of the mounted artwork with mat border included.
- Inside frame size (rabbet/opening): The internal frame dimension where glazing, mat, art, and backing fit.
- Outside frame size: Final external dimensions after adding frame moulding width.
- Fitting allowance: Small extra clearance to prevent a too-tight fit.
How to Measure Artwork Correctly
Precision begins with measuring technique. Use a rigid ruler or metal measuring tool, place your artwork on a flat surface, and measure to the nearest practical unit for your project. For large prints and premium framing, measure both top and bottom width, then both left and right height, and use the larger value if there is slight variation.
For deckled or hand-torn edges, decide whether you want to show the full edge or hide part of it under a mat. That design choice affects your mat opening and overlap values. If your print has a white border that should remain visible, measure only the intended visible image area and set your overlap accordingly.
Picture Frame Dimension Formulas
These are the core formulas used in this calculator:
Mat Opening Width = Artwork Width − (2 × Mat Overlap) Mat Opening Height = Artwork Height − (2 × Mat Overlap) Package Width = Artwork Width + (2 × Mat Border) Package Height = Artwork Height + (2 × Mat Border) Inside Frame Width = Package Width + (2 × Fitting Allowance) Inside Frame Height = Package Height + (2 × Fitting Allowance) Outside Frame Width = Inside Frame Width + (2 × Frame Moulding Width) Outside Frame Height = Inside Frame Height + (2 × Frame Moulding Width)If you do not use a mat, set mat border and overlap to zero. The package size then equals artwork size. This is common for posters, large prints, and minimalist framing styles.
Real-World Examples
Example 1: Framing a 16 × 20 print with a mat
Artwork: 16 × 20 in
Mat border: 2 in each side
Mat overlap: 0.125 in each side
Fitting allowance: 0.0625 in each side
Frame moulding width: 1.25 in
Results:
Mat opening: 15.75 × 19.75 in
Package size: 20 × 24 in
Inside frame: 20.125 × 24.125 in
Outside frame: 22.625 × 26.625 in
Example 2: Frameless mat design not used
Artwork: 18 × 24 in
Mat border: 0
Mat overlap: 0
Fitting allowance: 0.0625 in
Frame moulding width: 1.5 in
Results:
Package size: 18 × 24 in
Inside frame: 18.125 × 24.125 in
Outside frame: 21.125 × 27.125 in
Standard Frame Sizes vs Custom Dimensions
Many projects fit standard frame sizes, but custom work is often necessary for exact aesthetic balance or non-standard artwork. Use this quick table as a reference:
| Common Print Size (in) | Typical Mat Border (in) | Resulting Frame Size (in) |
|---|---|---|
| 8 × 10 | 2 | 12 × 14 (before allowance) |
| 11 × 14 | 2 | 15 × 18 (before allowance) |
| 16 × 20 | 2 | 20 × 24 (before allowance) |
| 18 × 24 | 2 | 22 × 28 (before allowance) |
| 24 × 36 | 3 | 30 × 42 (before allowance) |
Even when standard sizes are available, a calculator helps you confirm internal fit and final outside footprint before purchasing. This is especially useful when hanging multiple pieces as a wall set, where visual alignment depends on outside dimensions, not only image size.
Choosing the Right Mat Border Width
Mat border width is both technical and aesthetic. Narrow borders can feel modern and minimal. Wider borders often suit fine-art prints, galleries, and formal interiors. A common approach is 2 to 3 inches for medium-size pieces and larger for oversized art. You can also use weighted borders (for example, slightly wider bottom border) for visual balance.
Frame Moulding Width and Visual Weight
The wider the moulding, the larger the outside dimensions and the stronger the visual presence. Thin metal or narrow wood profiles suit modern photography and small pieces. Wider wood profiles can support heavier visual compositions, traditional art, and larger works. When planning grouped frames on one wall, include moulding width in every calculation to avoid spacing inconsistencies.
Common Picture Framing Measurement Mistakes
- Using nominal paper size instead of real size: Prints can vary slightly, so always measure the actual piece.
- Ignoring fitting allowance: Exact-size cuts can bind in the rabbet and cause assembly stress.
- Forgetting mat overlap: If omitted, opening can be too large and reveal unsupported edges.
- Confusing inside and outside dimensions: Order mistakes often happen when these are mixed up.
- Not accounting for orientation: Keep width and height consistent in portrait or landscape layouts.
Materials and Tolerance Notes
Wood and paper-based products can respond to humidity and temperature. Acrylic and glass can have manufacturing tolerances. For professional results, keep consistent tolerances across mat board, glazing, and backing. If your supplier provides tolerance specs, use those in your fitting allowance input. For valuable originals, use conservation mat board and UV-protective glazing.
When to Choose Custom Framing
Custom framing is usually the best option when artwork dimensions are non-standard, when color and moulding style must match interior design, when conservation-grade components are required, or when you need exact outside dimensions to align with architectural features or adjacent frames. A dimension calculator significantly reduces trial and error and keeps custom projects predictable.
Frequently Asked Questions
What frame size do I need for a picture with a mat?
Add the mat border to all sides of the artwork to get package size, then add fitting allowance for inside frame size. Finally, add moulding width on both sides for outside size.
Should mat opening be smaller than artwork?
Yes. A small overlap helps secure the art and hides edge irregularities. Around 1/8 inch per side is a common starting point.
Is glass size the same as inside frame size?
In many workflows, glass and backing are cut to the inside frame target with practical tolerance based on supplier guidance.
Can I use centimeters or millimeters?
Yes. Keep all inputs in the same unit. The calculator returns outputs in that same unit.
Can this calculator be used for certificates and posters?
Absolutely. It works for photos, posters, certificates, diplomas, art prints, and most flat artwork that fits a standard framing package.
Use the calculator above each time you start a framing project, and you can quickly move from concept to accurate ordering and assembly. A few minutes of precise math can save material costs, reduce delays, and deliver a cleaner final presentation.