How to gauge yarn totals

I am looking at a Drops Design pattern and the yarns needed are listed as 250-gr nr. What does this mean? I assume the gr is grams but I don’t know what nr means. The yarn for sale is listed as 110 m/120 yds. How do you translate that in yardage to know how much to buy?

Which Drops pattern are you looking at?
The nr likely refers to the color number of the yarn.

The pattern is Drops 89-17 Pullover in Alpaca and Cotton Viscose.

OK, for the Drops Cotton Viscose, a check on Ravelry shows that it’s 120yds/50 gm ball:
If you need 250gms, that’s 5 balls or 600yards.

Thank you, I was thinking it was something more complicated.