How to shrink a 100% cotton jumper

[Fivemoreminutes1]

I bought a really nice jumper in the sale, but it’s not true to the label size. I’d say it was actually a (women’s) size too big. Is there any way I can shrink it just a tad?

Nope, cotton fibres don't really shrink.

Cotton does shrink!

I'm not sure a deliberate shrink would work out well - you could end up with it misshapen.

The cotton might be pre-shrunk, but if you want you could try running it through a hot wash and then plunging it into cold water in a large sink and agitating it. Don't stretch it at all and don't hang it up to dry. Lay it on a towel, shape it and roll the towel up. Then let the jumper dry horizontally on a rack or something. None of this is guaranteed.
I'd just wear it loose. One size isn't too bad.

It definitely does!

Not sure how to do it deliberately though.

Wash it and then tumble dry it.

My tops that have accidentally, and annoyingly, shrunk tended to go boxy rather than overall smaller.