Estimate yarn needed

Someone recently put up a really good link to a video on two-handed two-color knitting.

I’ve been messing around with it and while doing it I’ve been thinking of things to make with this technique.

One question. If I know with a certain yarn and needle size I’ll need say 2 skeins to complete something in one-color knitting, trying the same with the two color technique (stranding or weaving the unused color behind the stitches) - does that mean the total amount of yarn I will need is x2? x1.5? What is a good rule of thumb? I know it is more because the fabric is certainly thicker due to the extra strands woven in the back.

I’ve been using yarn from my stash to figure this stuff out, but before I start something real, even something small like a hat, I want to make sure I don’t run out of the colors before it is finished.

Thanks!

Here’s the link -
http://www.philosopherswool.com/Pages/Twohandedvideo.htm

Hmm… I don’t know a way to estimate for fair isle, but maybe someone else does.