What is the smallest size of a piece of fabric that you would prewash?
Do you prewash jelly rolls and charms 5"x5"?

update:
Is it ok to mix in one project non-washed jelly and pre-washed others fabrics?

I've never bought anything smaller than quarter yard/fat quarter. I stay stitch the cut edges before I wash them.

I never prewash pre-cuts such as charm packs, jelly rolls, etc. I prewash
fat quarters and yardage. If I'm worried about bleeding I use some
Synthrapol and color catchers when I wash the quilt. Just be careful mixing
unwashed darks or batiks with lights. This needs special care.

Thank you, EasyPeezy! Is it ok than to mix in one project non-washed jelly and pre-washed others fabrics together?

Anything smaller than 1 yard I wash by hand with a little detergent, rinse well, squeeze out water and roll in a towel and air dry.
1 yard and larger goes in the washer for 6 minutes on gentle cycle. That is enough to wash out the chemicals but not enough agitation to fray and tangle.

Nothing smaller then a fat quarter. Sometime I just rinse a small piece in my sink.

I probably wouldn't pre-wash charms or jelly rolls because you lose the edges of fabric when they are washed. But when i get fabric scraps to do paper piecing projects, I usually throw them into a lingerie bag and wash them with the rest of my fabrics (and a color catcher). If not all materials in a project are pre-washed, you could have an issue with the non-prewashed fabrics shrinking while the pre-washed ones don't, but hopefully it wouldn't be a noticeable difference. Have fun quilting!

I don't buy anything smaller than a FQ. Ever.

Yes, I agree 100%.

You will probably have different shrinkage. I try not to mix pre-washed and non-washed but that's just me.