You can use cm in html/css, but I don't think you'll get the same real size at all devices. See some discussion at Stackoverflow:
https://stackoverflow.com/questions/4023192/div-width-in-cm-inch
https://stackoverflow.com/questions/41626418/how-to-set-physical-dimensions-like-actual-inches-for-elements
https://stackoverflow.com/questions/22166686/how-emulate-real-size-dimensions-in-css-javascript