Font size appears differently despite being the same size

I use the same font setting for my xterm in every system: fixed & 6x13bold for normal and bold fonts, however, the font look different in size on my desktop and my laptop.

I think it may be caused by that my desktop and laptop display have different DPI, but regardless, any way for them to look like the same size (with the same font setting), i.e., how to make my tiny font in my laptop to look normal?