EZGlassPattern guideHow much glass and copper foil do I need?
The arithmetic behind a stained glass shopping list, with a worked example you can follow with your own numbers.
Answer in 30 seconds
Glass: add up the area of each colour on the pattern and buy about 10 to 20% more for waste and breakage. Copper foil: about the total perimeter of all the pieces, plus a little extra. Lead came: about the total length of the seams, plus the border.
- Glass: area per colour × 1.1 to 1.2.
- Copper foil: sum of every piece's perimeter, plus about 10%.
- Lead came: interior seams counted once, plus the outside border, plus extra for joints.
The formulas
| Material | How to estimate | Notes |
|---|---|---|
| Glass (each colour) | Area of that colour's pieces × 1.1 to 1.2 | More waste with big sheets, streaky glass you want to match, or many curves |
| Copper foil | Total perimeter of all pieces × about 1.1 | Every edge is wrapped, so shared seams count twice |
| Lead came (inside) | Total length of interior seams | Each seam is one strip of H came |
| Lead came (border) | Outside perimeter of the panel | Often U or H came, or zinc |
Key takeaways
- Glass is bought by area per colour — add the colour's pieces up separately.
- Buy 10 to 20% extra glass — for waste between pieces and the odd bad break.
- Foil follows the perimeters — every piece is wrapped all round, so interior seams count twice.
- Came follows the seams — each interior seam gets one strip, plus the border.
Check a pattern, or make one from a photo.
Worked example (example numbers)
These are example numbers for illustration only. Your pattern will be different.
- Example panel: 12 × 16 inches, so the area is 12 × 16 = 192 square inches, in about 40 pieces.
- Glass for one colour: say the background pieces add up to 96 square inches. With 15% extra: 96 × 1.15 ≈ 110 square inches, roughly a 10 × 11 inch piece, though shapes rarely pack perfectly, so a 12 × 12 inch sheet is safer.
- All the glass: 192 × 1.15 ≈ 221 square inches, about 1.5 square feet across all colours.
- Copper foil: say the perimeters of all 40 pieces add up to 400 inches (about 10 inches each). With 10% extra: 400 × 1.1 = 440 inches, about 37 feet.
- Lead came instead: the outside border is 2 × (12 + 16) = 56 inches. Interior seams are shared by two pieces, so they are (400 − 56) ÷ 2 = 172 inches, about 14 feet of H came, plus 56 inches of border came, plus 10 to 15% for joints and offcuts.
Measuring the perimeters
By hand, run a string or a flexible tape around each paper template and add them up. It's slow but it works. A rough check: a roughly square piece of a given area has a perimeter of about 4 × √area; irregular pieces have more.
The shopping list in the EZGlassPattern pattern packet does this for you: glass area per colour with your waste percentage, copper foil length from the total piece perimeter, and lead came length from the seams. Make a pattern from a photo or check one you have.
Buying tips
- Buy sheets big enough for the largest piece in each colour, with margin around it.
- Match streaky glass from one sheet where possible; the next sheet may look different.
- Foil comes in widths; pick one that suits your glass thickness. Your supplier can advise.
- Keep offcuts: they're perfect for small pieces in the next project.
Step by step
- 1
Add up each colour's area
Sum the area of all the pieces in each glass colour, at full size.
- 2
Add waste
Multiply each colour's area by 1.1 to 1.2 for waste and breakage.
- 3
Add up the perimeters
Sum the perimeter of every piece for copper foil, then add about 10%.
- 4
Work out seam length for lead
Subtract the outside border from the total perimeter and halve it for interior seams; add the border separately.
- 5
Round up to what's sold
Round each amount up to the sheet sizes, roll lengths or came lengths your supplier sells.
Frequently asked questions
How much extra stained glass should I buy?
About 10 to 20% more than the pattern area for each colour. Buy more if you're a beginner, using streaky glass you want to match, or cutting lots of curves.
How do I calculate how much copper foil I need?
Add up the perimeter of every piece and add about 10%. Each piece is wrapped all round, so seams between pieces are counted twice.
How do I calculate lead came?
Interior seams are counted once: subtract the outside border from the total perimeter and halve it. Add the border separately, plus extra for joints.
How do I work out the area of irregular pieces?
Trace them on graph paper and count squares, or let software do it. EZGlassPattern's shopping list reports area per colour automatically.
Does the foil width matter?
Yes. Pick a width that suits your glass thickness and the look you want. Your supplier can advise for the glass you're using.
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