How do I change the text box size..? I don't want to use CSS.

Making the label larger or expanding the label doesn't change the text box size. How do I make them wider?

I am using the legacy mode as I want to create a horizontal form, but there is no visible option to change the box size...

Please Help.

Please note that some fields such as the short text entry and email fields will allow you to increase their size through the settings: 

If the file does not have such option then you may need to inject some CSS code to increase its size.