Often i run in to issues calculating how many pixels are 51x51 mm or 50x50 mm to resize photos for applying a government document like passport.
Here are few pre determined values
50x50mm - 300dpi = 591x591 pixels 51x51mm - 300dpi = 600x600 pixels
Here is the calculator to cross check the values.
https://www.pixelcalculator.com/index.php?round=&FORM=1&DP=1&FA=&lang=de&mm1=50&mm2=50&dpi1=300&sub1=+ausrechnen+#a1