Please look at the "size & fit" tab for the Gaiam clothing size chart . This should assist you in determining what size pant to order. The size 12 falls right on the line between a Medium or Large, so depending on your actual measurements, you should be able to determine what size to order. If you need further assistance, please contact a product specialist at gaiamprodspec@gaiam.com or 1-877-989-6321.