Pattern says knit in the round for 5". From what I’ve read online it seems I should measure from the underarm, but looking at my work, it seems long.
Just wondering if this might be the measurement from the shoulder?
Cheers - this is my first sweater, and baby!
Congratulations! 
When are you due?
Welcome to knitting help. Do you have a link for the sweater?
I’m assuming since you are knitting in the round, you are knitting from the bottom of the sleeve. Is this correct?
Welcome!
You’re right that the sleeve is usually measure from the undearm to the end of the cuff. Five inches sounds about right depending on the size you’re making.
Here’s a chart for baby sizes and also a key to the placement of the measurements that may help.
http://www.craftyarncouncil.com/babysize.html
http://www.craftyarncouncil.com/sizing.html
Thanks. Knitting the sleeve down - pattern:
Makes more sense that the measurement is from the underarm, taking a quick look at the as-yet unknitted side (which already has some of the top shoulder seam knitted- if that makes sense!). Thereby it is 5" from where I picked up the stitches, at both measurements.
I am due mid-Nov and I chose a green and grey tweed before I knew she was a girl. I may knit a second one in a buttery yellow if this one turns out! Thanks again for your help. I am sure I will be back as the collar seems to be the most challenging, having read some previous posts by knitters having trouble with it!
That’s an adorable sweater. Once you get it worked out to your satisfaction I could imagine a number of them in different colors for your new addition. Congratulations and enjoy the time and knitting.
I have that sweater in my queue for the next new baby so all your questions will be very useful. Congrats on the new baby!