EZGlassPattern · Free pattern checker
Is my stained glass pattern cuttable?
Drop your pattern below. Every piece is checked at the size you will actually build it, and anything glass won't do is marked in plain words, with a fix.
Updated
Photos never leave your device. The check runs in your browser.
Answer in 30 seconds
A pattern is cuttable when every line runs edge to edge and every piece can be scored and broken without turning a corner inward. The usual problems are sharp inside corners, deep inside curves, pieces trapped inside other pieces, slivers too thin to survive, crowded junctions and lines that don't close.
- Check at the real size: a piece that is fine at 24 inches can be a sliver at 8 inches, so enter the finished width first.
- Allow for the line: copper foil takes about 1 mm per line, lead came about 2 mm, so pieces end up smaller than they look.
- Most problems have a simple fix: add a break line, merge a piece into its neighbour, or close a gap.
The limits the checker uses
| Check | Flagged as tricky | Flagged as won't cut | Won't cut, Beginner setting |
|---|---|---|---|
| Thinnest part of a piece | under 9 mm | under 5 mm | under 7 mm |
| Smallest piece | under 250 mm² (about 16 × 16 mm) | under 100 mm² (about 10 × 10 mm) | under 196 mm² (about 14 × 14 mm) |
| Inside corner (how sharply the edge turns inward) | over 60° within 4 mm | over 80° | over 80° (warns from 43°) |
| Inside curve depth | deeper than 0.55 × its opening | deeper than 0.9 × its opening | deeper than 0.9 × its opening |
| Pieces meeting at one point | 5 | 6 or more | 6 or more (warns at 4) |
| Gap between two joints on a line | under 4 mm | under 2 mm | under 2.8 mm |
| Piece inside another piece | — | always | always |
| Line that stops short (open seam) | — | always | always |
The six things the checker looks for
- Sharp inside corners — a notch glass can't turn into. Fix: a line through the corner.
- Deep inside curves — a bay deeper than it is wide. Fix: a break line, or plan to groze it out.
- Pieces inside pieces — needs a cut that starts and ends inside the glass. Fix: a line out to the edge.
- Slivers, thin necks, tiny pieces — measured at final size minus the line. Fix: merge into the neighbour.
- Crowded junctions — too many lines at one point, or junctions too close. Fix: move or merge.
- Open seams — a line that stops short. Fix: close the gap to the nearest line.
Key takeaways
- Free, with no account — the cut check, the preview and the difficulty score cost nothing.
- Nothing is uploaded — your pattern stays in your browser from start to finish.
- Real size, real line width — every check uses your finished size and your method (foil or lead).
- Plain words, not jargon — each flag says what is wrong and offers a one-click fix.
- A difficulty score — so you know before you start whether this is a weekend piece or a long project.
Why patterns fail at the cutting table
Glass breaks along a score, and a score has to run from one edge of the glass to the other. Glass also wants to break in a straight line. Anything that asks it to do otherwise, like turning a corner inward or following a tight bay, ends in a crack running where you didn't want it.
A drawing doesn't know any of this. Lines that look elegant on paper can make a piece no one can cut, and the mistake only shows up once you've scored good glass. Checking first costs you a minute; finding out at the table costs glass. Our guide to cuts that are impossible in glass goes through each one.
How the checker works
- Drop your pattern. A PDF, a scan, a photo of a printed pattern, or an SVG. For a PDF, the first page is checked.
- Enter the finished size in inches or centimetres, and choose copper foil or lead came.
- Read the flags. Each problem is marked on the pattern with a short explanation.
- Fix with one click, or adjust by hand and check again. The difficulty score updates as you go.
What the limits are based on
The table above lists every limit the checker uses, measured on the finished piece after the foil or lead line is taken off. Widths and areas get stricter on the Beginner setting and looser on Advanced; the hard limits on inside corners and curves stay the same, because what glass physically can't do doesn't depend on who is cutting. They are sensible starting values, not a certified standard, and they will be tuned with working glass makers. If you know your glass and your grinder, pick Advanced to loosen them, and treat any flag as advice.
A flag is advice, not a ban. An experienced cutter can groze out a curve a beginner should avoid. The difficulty score reflects that: it tells you how much of the pattern needs careful work.
When you're happy with it
The check is free. If you also want the printable packet (a full-size tiled PDF, numbered key, colour key, shopping list and SVG), a Project Pass is $5 one-time for 30 days. See pricing for Lifetime. Before you print, read how to print a pattern at actual size.
Frequently asked questions
Is the stained glass pattern checker really free?
Yes. Checking any pattern, the preview and the difficulty score are free and need no account. You only pay if you want the printable pattern packet.
Does my pattern get uploaded?
No. The check runs entirely in your browser. Your file never leaves your device.
What file types can I check?
JPG, PNG, WebP, SVG or PDF. For a PDF, the first page is read in your browser; if your pattern is on a later page, save that page as a PNG and drop it in.
Why does the size matter?
Because glass doesn't scale. A piece 6 mm wide on a large panel can be a 2 mm sliver on a small suncatcher, and that won't survive cutting or grinding.
Can I ignore a flag?
Yes. Flags are advice. Experienced cutters can manage some curves and narrow pieces that a beginner should avoid, and the Beginner, Intermediate and Advanced settings make the limits stricter or looser.
Does it work for lead came as well as copper foil?
Yes. Pick your method before checking: lead came takes more width per line (about 2 mm) than copper foil (about 1 mm), so pieces come out smaller.
The check is free. Pay once when you print.
No account and no card for the cut check. A Project Pass is $5 one-time for 30 days of printable pattern packets, with no subscription. Lifetime covers everything, forever.
Related
- Make a stained glass pattern from a photoPhoto to pattern: choose a piece count, set the real size, fix flagged pieces, and print a full-size pattern.
- What makes a stained glass pattern good for beginners?What makes a pattern beginner-friendly, a checklist, and a free difficulty check for any pattern.
- Which cuts are impossible in glass?The cuts glass can't do (inside corners, enclosed pieces) and the ones that usually fail, with fixes.
- How do I print a stained glass pattern at actual size?Print at 100%, turn off fit to page, match the paper size, and measure the scale square before cutting.
- Copper foil or lead came: which should I use?Copper foil vs lead came: when to use each, line allowances, and how the method changes your pattern.
- Looking for a Pattrn-AI alternative?An honest comparison with Pattrn-AI (as of October 2026): what each does better, pricing, and the cut check.