<p>After a long time tweaking my new 3D printer I solved all the unexpected errors and I can print succesful pieces but I am facing a "problem", they are over sized, I found this problem trying to print a Raspberry Pi Case and an smartphone case, the printed pieces are bigger than the objects. </p>

<p>Here some related information</p>

<p><strong>Printer</strong>: Geeetech Prusa i3 Pro B</p>

<p><strong>Firmware</strong>: <a href="https://github.com/amendezcabrera/geeetech-prusa-i3-pro-b-firmware" rel="noreferrer">My GitHub</a> (Marlin)</p>

<p><strong>Software</strong>: Repetier Host with Slic3r</p>

<p>Does somebody know how could I solve it?
Thank you very much</p>

You have to know:
distance between belt teeth (usually 2mm)
number of teeth on pulley
motor step angle 1.8 deg?
microstepping count, probably 16?
Then you can enter all these numbers info the calculator here:
https://www.prusaprinters.org/calculator/