The pattern can be set to your gauge and size.
Several patterns can be used for the main piece, ribbing and the thumb.

Re gauge - I recommend leaving the same gauge for ribbing as in 1k,1p and for main part if you use a simple pattern like stocking stitch. Using the st st gauge for both parts will allow you to avoid changing number of stitches and will ensure a nice fit.

The number of stitches left for thumb is counted according to a general formula so make sure you try on the mitten right after leaving the stitches aside before continuing.

You can set any length of the ribbing, the width of the ribbing will stay the same as at the wrist level.

The pattern chart is shown in Firefox, Chrome and Safari. Unfortunately in Opera and Internet Explorer it doesn’t work right.
The pattern description is given at the bottom of the page.

Happy KnittinK! :)