The bathroom (toilet and shower together, but they are separated by a "narrow wall") take up approximately 4 square metres.

A standard bathroom at the SPT would occupy most of the room at the W. The regular room at the SPT is considerably larger than that at the W. Officially the W standard rooms are 26 square metres. I find that rather difficult to believe and must include the wardrobe and a 1 metre square entrance area seperate from the room proper. The SPT room is 31 square metres but the difference feels much greater than 5 square metres.

A typical room at the LM Piccadilly is around 25 sqaure metres and those rooms feel much bigger than those at the W. My guess is at the least the SPT and LM measurements do not include the bathroom as it is a separate space, whereas the W measurements do include it because it is part of the room. I couldn't swear to it because it has been a long time since I tried a standard room there, but I don't think that a standard room at the Park Lane is markedly different in size to those at the W.