they only had W31 available , which is my old size. i tried belther 828T in W30 but fit better in W29, and thavar 829B in W28 which fit perfectly. which means my size NOW is W29. im guessing that if your regular size is W31 then it should fit fine. i dont really know how much it will stretch. i dont think it runs larger in the waist like 811p does.