I think the main factor for Marlow sizing is width. I am 9.5D on the right and 9E on the left (US size). 9 probably would have worked if not for the width. I wear 9.5D which is a bit longer than I like while the toebox still feel a bit tight. So to sum up if you're Normal to narrow width than you can size down half, otherwise TTS. If you're truly wide than I'd say don't size up half, the last is just not for you.