Leave off the word “metre” and it doesn’t matter whether you’re using metres or cm. You’re “one eighty-six”. Is that a lazy way of saying “one [hundred and] eighty-six”, quite common when talking about numbers in the hundreds, or the lazy way of saying “one [metre] eighty-six [centimetres]”, a common shorthand similar to shortening “six [feet] five [inches]”? The answer is it doesn’t matter!