I have a vest pattern that calls for 2 balls of: Universal Yarn Mohair Mountain (200g/660 yds).
I want to substitute with a yarn that is the same needle size 6mm - but each ball is 100g/174 yds- how much do I need? Will it come out the same size or am I way off track?

the quick math is that the pattern asks for 1320 total yards, and you’ll need 8 balls of your substitution yarn to get that yardage (with extra left over). but remember to do a swatch to make sure it gives you the same gauge as the recommended yarn. even tho the one you want to use recommends the same needle size, it might act differently once it’s actually knitted. i might even get 9 balls, to be safe, and then return any unused ones after i was done…

2 balls @ 660 yds. ea. is 1,320 yds. 1,320/174 (yardage per ball of the other yarn)=7.59. I’d say you need 7 or 8 balls depending upon if you want extra just in case. If the gauge is the same the size should be the same, a different yarn could produce a fabric with a different hand or drape so that could influence fit and how well you like the FO.

Thank you both! I have 5 balls, how can I find a pattern to use this yarn?

if you’re on ravelry, you can search in patterns (use the advanced feature) - and then search by type of fiber, and/or fiber gauge (fingering, aran, bulky, etc), and/or number of yards, etc etc. it’s very comprehensive, but remember, it’s also just a recommendation. most patterns get made with yarn that’s different than what the designer used :wink: http://www.ravelry.com/patterns/search#craft= will get you started.

Will do, thank you!