Flanged insertion cord piping for cushion covers - what size in mm?

[ChocoHazelnutCroissant]

I have looked at tutorials for adding piping to cushion covers, but none indicate what size insertion cord I need.

eBay sells lots, but in different sizes, 2mm, 3mm, 5cm etc, and I don’t know which size to go for.

The cushion covers are (or will be) 32 cm x 52cm, so not too big and rectangular, if that helps you to help me.

I don”t want the piping to be too blindingly obvious, but enough that it sets off the colours on the cushion covers and gives them that finished look.
I’ve never used the stuff before, so that’s gonna be a feat in itself 😄.
Many thanks in advance for your advice 💐💐

I would go for 3, but that's down to personal preference mostly, could you order a length of each to try them out and keep them for future reference?

My logic is that 5mm seems very big and 2mm is more fiddly to work with than 3mm

@FlaviaAlbia, thanks.

I think your logic is sound. I don’t want my first attempt at piping to be fiddly, so it looks like 2mm is out.
I”ll look at the 3mm, that extra millimetre could be what I need.