Substituting yarn weights?

I’m getting ready to start this entrelac scarf, but using the aran weight yarn it calls for makes it too “thick” for my tastes (already started it once and then frogged it back)… I’d like to make it more lightweight and less “bulky”, so I would like to use a fingering weight variegated yarn I have.

I’m not quite sure how to adjust for the lighter weight yarn. Should I just use a smaller needle size, or increase the number of stitches to obtain the right size? (I’ve been told actual gauge isn’t very important for scarves, but I don’t want to wind up with something too thin width wise).

Any suggestions? I searched the forum but couldn’t find an answer other than a yarn converting calculator thats no longer available online.
Thanks in advance!!

Use smaller needles to get the fabric that you want, then increase the number of stitches by multiples of 6 until you get the width you want.

You’d just repeat the center squares more times to accommodate.

Thank you!!