Kniting help needed!

[Tatties]

I have been naughty and started to knit a baby hat without checking the gauge. The base circumference is about 40cms... how far should I knit before I start decreasing? I am guessing about 9-10 cms? Is there anywhere I can find a formula for working out this kind of thing? (Am I making sense?? )

[PrismManchip]

I knitted one recently
I don't think there's a formula - but you have to take roll into account if it's st-st
I think the pattern said knit 9.5cms so you are about right

[Tatties]

Oh fantastic, thanks
There is no roll at the bottom

[PrismManchip]

Ok then perhps not so long?
9.5cm was for a hat with a roll brim

[NotQuiteCockney]

I do about a third, and then a slow decrease. I do a lot of hats.

You want the decrease to start out slow, and then get faster, iyswim.

[NotQuiteCockney]

Wait, wait, if you're doing it without checking the gauge, how do you know how big around it is? Or have you measured it?

I always base the circumference on a (slightly) stretched circumference.