I have an XL set of Filson expedition weight merino wool long johns for sale. The are both forrest green in color. They are in excellent condition. I would say they would fit like a large with some heavy layers and fit like an XL with only light layering or next to skin. Here is the description from Filson:
Filson Long-Johns are made with the finest Merino wool for warmth, durability, and comfort. It's hard to understand why Filson goes through such a rigorous process to create their Long-johns until you try a pair for yourself.
Filson starts with long, fine fibers from specially-bred Merino sheep. Special sheep? Yeah, Filson never takes shortcuts. Then, Filson applies a "worsted" twist to the fibers to create a smooth, silky, itch free finish.
There are four reasons why wool long-johns are better than synthetics:
Wool wicks moisture away from the body while synthetics just redistribute it.
Synthetics wear out after multiple washings, while your grandpa is still wearing his old wool coat.
Unlike synthetics which can trap unpleasant odors, wool fibers absorb and neutralize odors.
Studies find that wool's greater adaptation to body temperature lowers the production of lactic acid and therefor increases stamina.
Filson's long-johns aren't only made of the best material possible, they are also designed effectively:
The top is cut extra long to stay tucked in even during vigorous activity.
Cut generously for ease of movement.
The neck and wrists are knit for maximum durability with an elastic waist band on the bottoms.
"SuperWashing" means your Alaskan Long-johns are machine washable (machine wash cold, gentle cycle, line dry).