I wasn't sure what an A4 is!
I worked in a print shop for years and didn't use that term. We just said 8 1/2" X 11". I didn't work the press area.
I do print on a full size 8 1/2" X 11" sheet, but always fill the sheet with other stuff.
See Attached - there is decals for five different projects on that single sheet.
Decal paper os only about $1.00 a sheet, but I hate to waste it.
Sometimes a model will sit and wait for another model that'll need decals. I'd just rather do all the decals at once.
TIP: One thing I've learned about home print decals. On a white background, the black print areas aren't a total opaque black. It's almost a little transparent.
Also, white background decal paper isn't a total opaque white. On a red background,
the white layer looks slightly pink.
I use Corel Draw to do my decals. I've had experience as a graphic artist and that comes into play. The learning curve on a graphics program is involved.
Anything I send out to others is usually on a PDF. If I remember, I try to include a 1" square box for print reference.