I´m between W30 and W31 most denims, I usually buy Tepphars W31 or W32, depending on the calf area fit. I don´t like them too snug.
For 824B I went with W31 as they are really comfortable overall. But be warned, the wash kinda smells, even after two times washing the smell slowly returns. Must be the bleaching or something.
They are a bit looser than same size 881W. I´d say they fit like 813W.
Hope this helps.