enter a persons height

You can use the Height Converter widget to enter a person's height. It can also convert the height from feet to cm with a click of a button.
http://widgets.jotform.com/widget/height_converter

To add a widget, simply follow this guide: How to Add a Widget to your Form
Here's a demo so you can see it in action: http://form.jotformpro.com/form/41943035117954? 

If you need further assistance, do let us know.