johan,
there's no standard size for spacers/grout lines.
You figure out what you like or what seems appropriate for the size of tile, the color of the grout, & the space available.
Can sometimes depend on what quality the tile is and whether it’s a square edge or slightly bevelled. Also how uniform they are in size.
Tiles can vary up to 2mm from quoted sizes.
Obviously in this instance a 2mm spacer could leave you struggling with some tiles.
You get the picture.
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