Frame and Mat Size Calculator

Frame and mat sizing is a two-step calculation that ensures your artwork is properly centered, protected, and visually balanced inside a frame.

Step 1 — Mat opening (the hole cut in the mat board): The opening is always slightly smaller than the artwork so the mat overlaps and holds the piece. The standard overlap is 1/4 inch on each side:

Mat Opening Width = Artwork Width − 0.5" Mat Opening Height = Artwork Height − 0.5"

Step 2 — Mat outer dimensions (= frame opening size): Mat Outer Width = Mat Opening Width + (2 × Border Width) Mat Outer Height = Mat Opening Height + (2 × Border Width)

Where:

• Artwork Width / Height — the actual physical dimensions of your print or painting
• Border Width — the width of the mat visible around the artwork (typical range: 2–4 inches)
• The factor of 2 accounts for equal borders on both left/right (or top/bottom)

What each variable means:

• Overlap (0.5" total) — prevents the artwork from slipping through the opening; most framers use exactly 1/4" per side
• Border width — wider borders give more “breathing room” and look more gallery-professional; narrower borders work for casual or small prints
• “Weighted” mat — some designers make the bottom border 0.25–0.5" wider than the top to counteract the optical illusion that equal borders look bottom-heavy

Standard mat border widths by art size:

• Up to 8×10 inches: 2–2.5 inch border
• 11×14 to 16×20 inches: 2.5–3 inch border
• 18×24 and larger: 3–4 inch border

Worked example: Artwork is 8 × 10 inches. Border width: 2.5 inches.

• Mat Opening = 8 − 0.5 = 7.5" wide × 10 − 0.5 = 9.5" tall
• Mat Outer Width = 7.5 + (2 × 2.5) = 7.5 + 5 = 12.5"
• Mat Outer Height = 9.5 + (2 × 2.5) = 9.5 + 5 = 14.5"

So your frame opening must be exactly 12.5 × 14.5 inches. Standard pre-made frames closest to this size would be 12×16 or 13×16, requiring custom cutting for a perfect fit.

Pro tip: Double mats (two stacked mat boards with different colors) use the same formula — calculate the inner mat opening, then add the outer mat border on top. The outer mat opening = inner mat’s outer dimensions + a small reveal (typically 0.25").