Yarn Quantity Help

[wawa]

Help talk me through this...I tend to overbuy yarn. Like, by a LOT.  Entire second blankets made with the leftovers from project purchases. 
I just always think, "well I don't want to run out...let's just round up" and end up with a metric shitton of extra yarn. 

Currently planning out a project - 
making this pattern - www.ravelry.com/patterns/library/rebel-ripple


which calls for 2100 yards of DK weight yarn in the form of one ball each of 9 colors of a 100 g/295 m yarn.

I want to make it with a fingering weight held two together that comes in 50 g balls with 186 yards.  By yardage what i need is 3 balls each of the colors.  By weight it's 4.  
Can this be the day I DONT' buy twice as much yarn as I need?  Should I just get 27 balls of yarn?  By yardage, that should be good. (~2500 yards if held double)  
because of how the pattern works, so it'll be obvious after the first color change whether I have enough yarn of each color, so no yarn chicken.  

27 is the right number.  Right??  Not 36?

[aprilsails]

Yeah I would go with 27 if you use the same size needle it should be just fine to go by yardage. Your blanket will wind up a bit lighter than the original, but DK weight vs length is pretty variable depending on the manufacturer (and don’t get me started on sport).

[wawa]

ok i'm doing it! yarn purchased.
(see, I just needed one person to validate me. mostly so I can come back and blame you aprilsails , if it's not enough)

I'm excited about this one. it's a baby blanket and when the mom-to-be told me her preferred color combo I was a bit meh on it just because it's not the kinds of colors that grab me, but then an ad popped up on facebook with that colorway in a bunch of soft shades of a nice cotton and I was like, "oh, that'll do. that'll do QUITE nicely."  Inspo pic: 


terrible long skinny picture of actual colors purchased attached. 

Of course I have to set aside my Husband Blanket project to do it...it'll be my first test of picking back up the long term project after stepping away and not letting it be a UFO.  Not that he would ever let me live it down if I didn't pick it back up.

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