Best way to have user choose between units of measurement

What's the best and most intuitive way to have a user choose what units of measurements to use throughout the fields he is filling out ? I have a form with several steps. And I was thinking somewhere in the beginning to have the user choose what system he's gonna use. if he chooses one system, then all of the fields in the other steps will change from : kg to lbs , inches and feet to cm .

What would be the best way to design it ? A radio button or a button or to segment it and have him choose in the beginning or is there any other best way?