Getting Stained Glass To Fit

Measuring For A Window

If you want to make stained glass windows that are going to fit into a specific place, it’s important to get the measurements accurate right from the beginning. It’s best to take the measurements even before you start your design, so that you can scale the pattern up easily to fit.

Do you need to measure?

If you are learning how to make a stained glass sun catcher, or a hanging panel that doesn’t need to fit in a window frame, then you can skip the measuring and go straight to Designing or Finding a Pattern.

1. Measuring The Window Opening

This is quite hard to describe, but isn’t hard to do once you break it down logically.

If you think about the task in three stages, it might help. You need:

– the size of the opening – the Tight Size

– the adjustments needed to make room for putty – the Fitting Size

– the measurements needed so that the whole of your design is visible – the Sight Size

section drawing showing different measurements
Three measurements needed to measure a window

– the Tight Size = the exact size of the hole that you want to make your panel for.

Have a good look at the window or door panel. You can probably see that the sheet glass is held in with either putty or a wooden rebate. The drawing above might help. You need to measure not only the glass you can see, but to the edge of the frame underneath the putty or wooden rebate.

This will be your largest measurement.

– the Sight Size = the size of the glass area that you can actually see.

If you have beading or putty holding the existing glass in, measure to the edge of the beading. The diagram above explains this. You need to know this measurement so that when you make your panel, the whole of your design will be visible.

You wouldn’t want the tip of a leaf to be chopped off behind beading, you want it all to show.

Some people call this the Daylight Size.

This measurement is your smallest measurement.

2. The Fitting Size

Now you need to work out the third and most important measurement – the Fitting Size. This gives you the measurements for the outside edge of your stained glass panel.

If you imagine going to a glaziers and asking them to cut you a piece of glass for a window, they never cut the exact size of the opening, they always take a bit off around the edge so that there is room for the putty to fit in around it.

diagram of different measuring lines
Diagram showing three window measuring lines

– Work out the Fitting Size by subtracting 1/8th inch or 3mm from each edge of the Tight Size.

The drawing above might help you visualise what I’m talking about.

This set of measurements will be somewhere in between the Tight and Sight Size.

Once you’ve got your fitting size measurement, you can forget about the tight size altogether.

3. Things to Remember

– Make sure you measure all four sides. Some windows are not geometric!

– If you are making a pair of windows, measure both. Never assume they are the same size, especially in older buildings.

– Measure the angles to make sure the window is square.

4. Which Measurement Do I Use For Cutting The Art Glass?

Very good question. The answer is that you haven’t got that measurement yet…

You have the Fitting and Sight sizes, which are all you need to get started on your design.
But once you start making your pattern – or Cutline – for cutting the art glass pieces, you will need to take another set of measurements for the outside edge. If you look at the drawing below, you’ll see what I mean.

diagram with brown cutline detail
Drawing showing measurement for stained glass pieces

You can see from this diagram that you can’t use your Fitting size for cutting glass to, otherwise there will be no room for the lead or zinc came, and your panel will end up too big. So you must cut your glass smaller to allow for the border lead or zinc.

How much smaller depends on how wide your border lead is. Let’s use the example of 1/2inch (12mm) lead. This is the width that is usually used to edge window panels.

You want to cut your glass to the inside of the heart, so you need to measure 1/4inch (7mm) in from each edge of the Fitting size for your art glass cutting pattern (Cutline).

This Cutline will be in between your Fitting and Sight size.

Check Your Measurements

It seems very complicated when I explain it, but if you take it a step at a time, you’ll see that it’s quite logical and obvious. I always get all these measurements worked out – and checked three times! – at the beginning of a project. I write them all down in my sketchbook clearly, making sure I label them.

Once you’re happy with them, and are confident they’re accurate, you’re ready for Designing or Finding a Pattern.

31 thoughts on “Getting Stained Glass To Fit”

  1. Hi Just wondering if you can advise on measuring for a half moon semi-circle window. I measure the width and the height (at tallest point). If it’s symmetrical the height should be half the size of the width. Is it that straightfoward? Would you assume that most semi-circle window apertures are more or less symmetrical? Any other tips for this shape. Thanks so much

    • I’d never assume anything with windows, whatever shape Siobhan 🙂 The very best foolproof method is to make a template. Thanks for your very good question.

      • Hi Milly, I am also needing to know this, as the window I am replacing has a semi circle as the top of a rectangle, if that makes sense! I also need to replace an oval.
        What is the best way to make a template when the existing window is in situ?
        Thank you : )

        • You can use thin white paper (like very heavy tissue paper) initially. It’s easy to manipulate taped against the windowpane, then trace and cut as needed to fit. I always mark which direction is which before removing, and make a more rigid version with cardboard from that to make a final check.
          I hope that helps Sam.

  2. I am making 26″ x 33″ window panels with 9 panes that are
    8″ x 11″ each using 1/2′ flat came. The panels will be in a wooden frame on an outside porch. Should I cement /putty both sides of window panels? Thanks

    • Yes, putty both sides Don. It’s actually hard NOT to putty both sides as it seeps through. It will make it much more rigid and stable.
      Good question, thanks for asking.

  3. Thanks for this helpful guide to measuring -something I’m not great at! I am designing two panels for my bathroom door and have a few questions I wonder if you can help me with..
    The panels are each 100.5cm x 24.5cm. I have designed the pattern as pictorial with a lighthouse on one side, sea cliffs and rocks on both which has been a challenge!
    My questions are do you think it will be strong enough as a door panel if I do it completely with copper foil without lead/zinc round the panels? I think it too narrow to do the project in lead and am happier working with copper foil.
    How many pieces right across would I need to strengthen it. I have strengthening “tape”
    When setting it in to the space do you have a sealant you’d recommend which I presume would strengthen it as well as stop movement. I had thought of placing a sheet of clear glass under it but would prefer the panel on it’s own.
    I’d be grateful for your advice if you have time.
    Many thanks Liz.

    • Sounds a great project Liz. I’d always put lead/zinc around the edge for any panel of any size, for stability. This is especially important in a moving panel, like a door. You can do the window itself in foil. Use ReStrip (or similar) every 12″ or so, design dependent. You can putty them in or silicone in.

      I hope that helps, good luck and send a photo when you’re done!

  4. I have a question about sizing for a glass window pane that is 11.5 inches. I don’t plan to enclose the window pane glass in zinc or lead just use silicone to hold the glass pane in the window frame. So, would I stop at the fitting size measurement (taking an 1/8 inch from each side) or what do you suggest.

  5. Hi Milly thanks for your great site. I am confused about the different sizes of outside lead and inside lead. I know the outside border for my project is 12mm 1/2 flat and glass size is 3mm. The only inside lead size I can find is 8mm 5/16 flat. Would this be right for the size of glass?
    Many thanks Fiona

  6. Hello ! Great site.
    I’m a bit confused with the fit of lead came and glass. I’m making a terrarium, using came with a 5mm channel (the smallest I could find) and 2mm thick glass.
    I understand that the black putty will take up some slack, but unsure if the glass is too thin.
    Is this likely to be a problem ?
    Many thanks

    • Hello Ron, 2mm glass is picture framing glass so it is thinner than normal (3mm). It will leave more room in the channel which you can fill with cement so it shouldn’t be a problem per se. However, it won’t be as robust as 3mm glass so if you have some fairly large pieces I’d go with 3mm.
      The terrariums I’ve made have been using the foil method as I find it easier for 3D objects.

      Glad you like my site, thanks 🙂

  7. Hi Milly, thankyou so very much for responding to my question about how to measure pattern for a specific size and accommodating the zinc. Was super helpful!! Love your site. Have been making glass for 40 years and still learning!!! Thanks so much

  8. Hi Milly,

    Have you used the Gemini Taurus 3 saw? If so, what do you use for your pattern material? Mylar, cardstock? Any information will be helpful.

    • Yes I do use these saws for certain cuts Karyn. I use permanent pen with vaseline over to guide the cutting. I hope that helps.

  9. Im building a 18”x 90” window and dividing it into 3-18” x 30” panels. Two questions: what size U zinc would you use to frame it and what size lead to build it?

    • 1/2″ zinc or lead came for the edging.
      The internal lead came size is up to you and depends on what you want to emphasise and your design. You can use a variety of widths for this. Anything above 5/16″ / 8mm is a bit heavy on the eye and hard to manipulate so I wouldn’t advise any wider than that.
      I hope that helps.

  10. Hi, I’m making panels to go above the opening/doorway between my lounge and dining area. . Do I still need to use thick came at the edges or could I use the finer came that I will use throughout the piece? Not sure if it’s just a personal coice thing, or a structural need.
    I’ve had a 10 year break from this. Feeling nervous about measuring up. This has been so useful . Thank you so much.

    • I would use the wide lead came, yes. It gives you room for a little bit of leeway with your measuring and fitting, as you can shave the H came to fit when you install. Usually the came is covered by beading/quarter rounds, so you don’t see it.

      That sounds like an exciting project Judith. I hope that answers your question.

  11. Thank you for suggesting that you need to make sure and measure all four sides of the window. My husband and I are wanting to get a stained glass window for our kitchen. I’ll have to look into finding the best company to make and install this for us.

  12. Milly: your website is very informative and clearly stated. I have been away from stained glass for 20 years but anxious to get back at it. I would like your recommendation for puttying a finished piece. Have looked at recipes for mixing putty but would prefer using ready mix. Do you have a recommendation. After putty dries do you use a whiting powder to clean the stained glass work?

    I appreciate your recommendation and response.

  13. Hi Milly,
    Great description, very informative. I have one question:
    I am making a stained glass panel to fit into my front door. There is a difference of 72mm between the tight and sight size, this is much thicker than the border lead so what do I do in the bit you don’t see?

    • The ‘Sight’ size is just for design purposes. So you would make your window to the ‘Fitting’ size but make sure that everything you want to actually see is within the ‘Sight’ size. For example, if you had a dog’s nose close to the edge you would want to make sure that the nose isn’t visually chopped off by being behind the fittings. The nose needs to be within the ‘Sight’ size.
      The glass beyond the ‘Sight’ size makes the window fit. I hope that explains it.
      Great question Joanna, thanks.

  14. I found the examples of soldering lead joints ineresting and informative also I liked the was to measure, cut and fit a glass panel into an area.


    Gary Skipper


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