The measurement every frame shop uses for pricing. Width plus height, in inches. Here's the formula, a worked example, and the quick calculator.
United inches (UI) is the sum of a picture frame's width and height, measured in inches. A 16×20 frame is 36 united inches. A 24×36 frame is 60 united inches. It's a single number that captures the size of the frame and — critically — tracks with how much material the frame actually consumes.
United Inch Formula
united inches = width + height
Simple as it looks, united inches are the backbone of custom frame pricing. Almost every pricing model — from a corner shop in Des Moines to a gallery in Manhattan — is built on UI. Moulding catalogs quote prices per UI. POS software calculates job totals per UI. It's the universal unit.
Enter width and height. Get united inches, perimeter, and pricing estimates at common rates.
Framing materials scale with perimeter, not area. A 16×20 frame and an 8×40 frame both have the same 72-inch perimeter — and very similar material requirements. Both need the same moulding footage, the same approximate mat border, and roughly the same glass edge length.
Using square inches would make that 8×40 frame look bigger than it is. 320 square inches vs. 320 square inches — fine. But compare 16×20 (320 sq. in.) with 22×22 (484 sq. in.). The bigger square frame looks 50% more expensive by area, but costs roughly the same in materials because the perimeter difference is only 7%. United inches captures that. Square inches doesn't.
Common custom frame sizes and their united-inch totals:
| Frame Size (inches) | Common Use | UI |
|---|---|---|
| 5×7 | Small photo, memento | 12 |
| 8×10 | Portrait photo | 18 |
| 11×14 | Art print, certificate | 25 |
| 16×20 | Standard art print | 36 |
| 18×24 | Poster, art print | 42 |
| 20×24 | Family portrait | 44 |
| 22×28 | Movie poster | 50 |
| 24×36 | Large print, poster | 60 |
| 30×40 | Gallery piece | 70 |
| 36×48 | Large statement piece | 84 |
Custom frame pricing typically runs $2 to $8+ per UI, depending on the moulding, mat, and glass. A simple frame with a basic moulding and single mat might run $3–$4 per UI. A gallery-quality frame with museum glass, a triple mat, and a high-end moulding can exceed $8 per UI. Translated: a 36 UI piece ranges roughly from $108 to $300+ depending on specification.
These numbers vary by region and shop, but the structure is consistent: UI times a rate per UI, plus or minus service fees (chop, join, float mount, shadow box). When a customer asks "how much for a 16×20?", they're really asking how much your rate-per-UI is.
If UI is the size, the actual moulding needed is longer. The math: moulding length ≈ 2×UI + (8×moulding width). The first part is the perimeter. The second part is the miter allowance — each of the four corners needs extra length to land correctly at 45 degrees.
A 36 UI frame with a 1.5" moulding needs roughly 72 + 12 = 84" (7 feet) of moulding. A 60 UI frame with the same moulding needs 120 + 12 = 132" (11 feet). The bigger the moulding, the bigger the miter allowance — which is why chunky gallery mouldings use more material than their UI alone would suggest.
The full moulding calculator does this math exactly, including kerf for each saw cut.
UI tells you how much material a single frame needs. It doesn't tell you how to cut 20 orders across your moulding stock without wasting a full stick. That's a separate problem — and the one that costs shops money every day.
RailChop takes your full day's cut list, packs it across every available stick, factors in remnants you've already saved, and returns an optimized plan in under a second. Right at the saw.
For united inches used in pricing, measure the opening — the visible size of the artwork or mat window. This is typically rabbet-to-rabbet for framing, or the sight size for matted work. The outside dimension of the frame (point to point) is larger because of the moulding width on each side, and shops generally don't quote off that measurement.
Yes, united inches is always inches — that's where the name comes from. Metric shops typically convert: a 40×50cm frame is 15.75×19.69 inches, or roughly 35 UI. Some international shops use "united centimeters" (width + height in cm) as a direct equivalent, but it doesn't translate to US-based moulding catalogs cleanly.
For pricing, UI is typically the opening (the visible artwork size). Some shops quote on the outside dimension (the full frame) — but this isn't standard and it penalizes customers who chose a chunkier moulding. When you see "UI pricing" on a moulding catalog or a POS system, assume it's the opening unless explicitly stated otherwise.
Octagonal, oval, and other non-rectangular frames don't fit the UI model well. Some shops approximate by using the bounding box (the smallest rectangle that contains the frame). Others charge a flat rate or a per-foot rate for specialty shapes. If more than 5% of your work is non-rectangular, UI alone won't cut it for pricing.
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