Calculate mat opening, mat cut size, and outer frame dimension for any artwork. Supports optical-center weighting — the subtle adjustment that makes a frame look balanced.
A matted frame has four measurements to track: the artwork size, the mat opening (slightly smaller than the artwork so the mat holds it in place), the mat outer size (opening plus borders), and the frame outer size (mat outer plus moulding width on both sides). Here's the math:
Mat Math
opening = artwork − (2 × overlap)
mat outer W = opening W + left border + right border
mat outer H = opening H + top border + bottom border
A standard overlap is 1/8" per side — so the mat opening is 1/4" smaller than the artwork in both dimensions. That's tight enough to hold the artwork but loose enough to avoid visible ragged edges.
Equal borders (2" on every side) put the artwork at the geometric center of the mat. But the human eye doesn't see it that way. Because we perceive more visual weight toward the bottom of a rectangle, an equally-bordered frame actually looks slightly bottom-heavy.
The fix is optical center: make the bottom border 10–15% wider than the top. For a 3" top border, the bottom becomes 3.3"–3.45". The math says it's asymmetric, the eye says it's centered. This is the mark of a frame built by someone who's been doing it for a while.
Enter artwork size and border widths. Get mat opening, mat cut size, and frame outer dimension.
A quick reference based on artwork size:
Signed prints. A wider bottom border (often 1.5–2x the top) gives the signature room and makes it feel like part of the composition rather than crammed at the edge.
Documents. Diplomas, certificates, and legal documents look more formal with a wider bottom border. Same rationale: the printed text often ends near the bottom, and equal borders make it look like the text is too close to the frame.
Panoramas. Wide landscape photos benefit from wider side borders to give the horizontal composition emphasis. Top and bottom stay tighter.
Double/triple mats. When using multiple mats, the reveal (the width of each mat showing through) is typically 1/4" to 1/2" between mats. The outer mat's borders dominate the visual hierarchy.
Bigger mat borders mean a bigger finished frame, which means more moulding, which means more cost. A 16×20 artwork with 3" borders becomes a 22×26 frame — 48 UI. The same artwork with 4" borders becomes a 24×28 frame — 52 UI. That's 4 more UI of frame perimeter, plus a larger mat, plus larger glass. Each extra inch of mat border has a real material cost.
For budget-conscious customers, a rule of thumb: keep mat borders under 3" unless the artwork needs the extra space. For gallery work where visual impact matters more than material cost, lean wider.
Most shops' mat-cutting workflow is fine for one order at a time. Where things slip is when you have 10 orders and need to get matboard cuts and moulding cuts through the shop efficiently — without running out of either.
RailChop handles the moulding side: scan, optimize, cut. Your matboard workflow stays the way it is — RailChop doesn't try to replace your mat cutter or CMC integration.
It's the industry standard for a reason: tight enough to hold the artwork in place behind the mat, loose enough to tolerate minor irregularities in the artwork edges and small shifts from matboard expansion. 1/16" is possible on square-cut, dimensionally stable paper — but risky if the matboard or artwork cups even slightly.
From the mat opening. When customers say "I want a 3" border", they mean 3" of visible mat around the artwork. Since the mat opening is cut 1/8" smaller than the artwork, the actual distance from artwork edge to mat outer edge is 3" + 1/8" = 3.125". This is calculator-handled automatically.
In a float mount, the artwork sits on top of the mat with all edges visible — instead of behind a mat with an opening cut. The formula changes: there's no opening to cut, the mat is sized entirely by the finished presentation, and the artwork's deckle edges (if any) stay visible. This calculator doesn't cover float mounts — the design decisions are different.
Start from the outer mat (furthest from the artwork) and work inward. Each inner mat's opening is wider than the next — the difference is the "reveal" visible between the mats. Standard reveals are 1/4" or 3/8". Calculate the outermost mat's opening the same way as a single mat, then subtract 2×reveal for each inner mat's opening.
Scan the work order, optimize the cut plan, track your remnants. On the App Store today.
We’ll email you when the Android app is live. No spam.