Need to borrow someone's math brain.

I've had a whole cup of chocolate-milk-and-Bailey's, which has killed what little math brain I have, apparently. Normally I can do basic algebra but this just isn't computing.

So I'm trying to make scarves based on this and this. So the images come out looking like this:

D I S T R I C T T W E L V E
[ identify ]

Now, I can see that the dimensions in pixels are height=25 and width=172.

1. When I'm double-crocheting one strand, I get 4st=1in long, and 2st=1in tall.

2. When I'm double-crocheting two strands, 5st=2in long, and 5st=4in tall.

In each case I'm trying to make the scarf to scale. How many stitches across would I need to do to make a scarf to scale? If I'm making no sense or if you need more information, just say so. If you're not a math person, just disregard this barely-even-tipsy-just-more-math-stupid post.

Thanks. <3

Edit: I'm going lengthwise (aka I'd be going 25 st at a time for 172 rows if I were single-crocheting, which I suppose I could do to avoid the math headache but single crochet takes forfuckingEVER and double crochet is more fun)...okay, going to bed now.