Definition: The intentional "wiggle room" built into a frame's internal dimensions to accommodate natural sizing variations in art, mats, glazing, backing, and the frame itself. Allowance ensures that the assembled package fits without forcing materials, which could cause damage or warping.

Overview

In framing, allowance is not simply empty space - it is a calculated tolerance. Because artwork, mats, glazing, and backing boards are rarely cut with absolute mathematical precision, framers add a fractional amount of extra space when designing or fabricating a frame. This ensures that the completed stack can be inserted into the frame rabbet and seated securely without undue stress.

Industry standards for allowance may vary by manufacturer and by material, but the principle remains the same: to create a balance between snug fit (which prevents rattling and shifting) and safe clearance (which prevents buckling, cracking, or over-compression of the components).

Why Allowance Matters

Dimensional tolerances: Cut mats and glazing often deviate slightly due to blade kerf, humidity, and operator handling.
Material expansion: Paper, wood, and plastics expand or contract in response to temperature and humidity.
Assembly efficiency: A frame without allowance can lead to difficulty seating the stack, wasted time, or potential damage to the artwork or glazing.
Structural stability: Correct allowance reduces rattling or visible gaps once the work is on the wall.

Standard Practices

Frame Allowance: Typically between 1/16"-1/8" (1.5-3 mm) is added to the artwork size to determine the frame's "cut size." This ensures the full package slides in smoothly.
Mat Allowance: Mat openings are generally cut 1/8" smaller than the artwork dimensions to overlap edges for hold-down, but the mat's outer dimensions receive allowance to match the frame size.
Glazing Allowance: Acrylic and glass should not be force-fit; the same frame allowance applies so that the glazing sits without stress.
Backing Board Allowance: Foam core and backing materials are trimmed slightly smaller than the frame's inner dimension for ease of fit.

Calculating Allowance

Allowance is often expressed as frame size = artwork size + allowance. For example, if artwork is exactly 16" x 20" and the framer uses a 1/8" total allowance, the frame's cut size might be 16 1/8" x 20 1/8". This ensures the mounted artwork, matting, glazing, and backing fit comfortably without strain.

Conservation and Archival Considerations

Overly tight frames can create significant conservation risks. Pressure against glazing can cause Newton's rings or surface abrasion, while compression of paper edges accelerates deterioration. On the other hand, excessive allowance can cause artwork or mats to shift, leading to skewed presentation or mechanical damage. A carefully balanced allowance is therefore an essential conservation decision, not just a mechanical one.

Common Misconceptions

"Tighter fit equals better protection." In reality, too little allowance can cause warping, cracked glazing, or abrasions.
"Allowance is the same for all materials." Materials like acrylic, wood, or paper expand at different rates, so allowance values should be material-specific.
"Allowance is only a manufacturing concern." Framers actively adjust allowance during design and cutting - it's part of quality craftsmanship, not just factory tolerances.

Identifying and Specifying Allowance

Manufacturer guidelines: Many moulding suppliers build in a standard frame allowance (often 1/8"). Framers must know this to avoid double-counting.
Custom cutting: When cutting frames manually or via computerized equipment, framers can specify their own allowance margin.
Terminology check: Some suppliers list "frame size" (inside opening after allowance) versus "art size" (tight dimensions). Misinterpretation can lead to fit errors.

Framing Workflow Tips

Confirm whether your supplier's quoted "frame size" already includes allowance.
Always dry-fit mats, glazing, and backing into the rabbet before final assembly.
Consider seasonal humidity - more allowance may be needed for works in environments with high fluctuation.
Label custom projects with allowance notes for future reframing consistency.

Allowance