Vitruvius counted in modules: the lower diameter of the column. Doric is stocky, Corinthian tall and leafy, Ionic the volute in between. Enter a diameter in metres; the plaque returns shaft, capital and full order as a Renaissance treatise would.
Modules after Vignola’s canon (the one British and American architecture schools still recite), which tidies Vitruvius and Serlio into round numbers. Greek Doric at Paestum is heavier than this; Roman Corinthian on the Pantheon is not a textbook. Use the plaque for a reconstruction sketch, not a listed-building consent.