Is this a blanket or a dog coat? Dogs do not use blankets except to lay on, so I assume this is a coat you are talking about. Dogs are different sizes, you can't go just by the breed. If this is a puppy then it will be much smaller than a full grown dog. Lab's are a bigger breed, but it would be better if you had the measurements.

I said blanket which I mean to lay on.

I found the following information on Orvis' website. Maybe it will help.

Medium 37" x 24" outside dimensions, dogs up to 70 lbs.
Large 43" x 30" outside dimensions, dogs 70-100 lbs.
X-Large 54" x 35" outside dimensions, dogs 100+ lbs.

That should help.
Thank you so much for your help.