My feet are certainly not a feet long. More like 25 cm or so. But as another commenter already said, I can measure ~175 cm using my arm's reach easily, matchboxes are standardised as 5 cm long, the width of my palm is about 8 cm, distance from my fingertips to my elbow is around 50 cm and the distance from ground to approx. my navel is 1 meter.
Plenty of ways to get an approximate metric measurements without a ruler or measuring tape.
And it's much easier to convert from cm or mm to m (or vice versa) than to convert between ft and inch or ft and 1/8 of an inch or whatever weird measuring standards the US-ians use.