People often say they would like to order or make a standard size gobo. The problem with this is statement is, that there is no standard size for gobos.
There are certainly some gobo sizes that are more popular than others, but there is no standard size in the Gobo world.
The reason is that each lighting instrument that projects gobos takes it’s own unique gobo size, and because sizes are different, some gobos can fit much more writing, or a larger design, than others can. There are over 75 different gobo sizes and each fixture takes it’s own unique gobo size. Gobo sizes are usually referred to with a corresponding letter, like A size, B size, M size, D size, or even Q size. If you do not know the name or the size of gobo you need, the two sizes that you will need are, the OD (outside diameter), and the IA (image area), the IA is where the design will be placed on the gobo. For example, A size gobos have a 100 mm OD, and a 75 mm IA, but the Q size gobo for the GoboMan projectors, has only a 22mm IA, and a 49 mm outside diameter, so obviously the A size will fit much more writing and a larger design than the Q size gobo. That said, you can still get up to 13 letters on a Q size gobo depending on the font used. You don’t want to try to get to much on a gobo because you can end up with tiny letters that don’t project a lot of light .

There are many websites online that provide lists of which lighting instruments take which gobo size and what the exact measurements are. There must also be a match between the gobo size and the correct sized gobo holder. This is also not a standard size. A good example of this is the ETC Source Four, which can take either a A size gobo holder or a B size gobo holder and also a glass pattern holder, so not all gobo holders are the same, or a standard size.