Weaving a seagrass seat...  

Not sure
is that what you're using with your Kai Kristiansen desk? That's my favorite Hvidt and Mølgaard chair!

I found them together. I...
I found them together. I have an incredibly comfortable Eric Buck #50 arm chair that I currently use.
When I've got the Hvidt & Mølgaard restored (It needs a cleaning badly, and the upholster is a joke), I will have to see if the seagrass is as comfortable as a floating seat.

I did a set of these
a long time ago. I don't remember the exact diameter of the original cord, I just remember that when I went to order it, it wasn't available so I settled for a much smaller diameter cord. It was ok but I wouldn't do it now.
I think 3/16" is about what the original was just from what I remember of the look of it. You might want a more accurate answer than that, though. (haha)
Are there any detail shots on Dibs where you could calculate the cord diameter?

I just measured several vinta...
I just measured several vintage one using a dial caliper. The seagrass on them is much less consistent than papercord. Varying from 1/8" to 3/16". Mostly though, they are just a hair under 3/16".

Thank you tchp!
Thank you tchp!

Per Thorsten Jacobsen of...
Per Thorsten Jacobsen of Soeborg Moebler:
"
The original sea grass cord had a diameter of approx. 4,5mm.
"
Which is the same as tchp's measurements. I think this question has been definitively answered!