Need some help creating a pattern

So there was a yarn sale and I got a bunch of this yarn because its nice and soft - in ruby and sable - to make a small lap blanket for my boyfriend’s couch. How do I figure out if I bought enough? I’m thinking of using the ruby as the main color and putting in a stripe of the sable here and there.

There are a lot of resources on line about estimating yarn requirements for various clothing items, but I wasn’t able to find any for blankets. So, my advice would be to look around at patterns for the yarn you have or yarns of the same weight similar to the one you would like to make and see how much yarn it requires.

Just a thought, you could join us over at the JanKAL and do a log cabin with large red logs and small sable logs and then just stop knitting when you run out of yarn or reach the size you want (Whichever comes first).
There are some other patterns there too if you want to look to see if something catches your fancy.