how i give the square size of the chessboard for calibration?

Question

I am using python 3 and opencv3.6 and i am performing a stereo camera calibration using a chessboard.

I was asking me, there is a moment where i have to give the square size? I checked the opencv tutorial but it wasn't very clear. I would like a confirm.

If the criteria i am using is :

criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001)

The 30 stays for the square size??

The function i am using are cv2.calibrateCamera, cv2.stereoCalibrate

 ret, mtx, dist, mtx2, dist2, R, T, E, F = cv2.stereoCalibrate(objpoints_l, imgpoints_l ,imgpoints_r, mtxL, distL, mtxR, distR,
                                                          gray_l.shape[::-1],
                                                          flags = flags,
                                                          criteria = termination_criteria_extrinsics )

Thanks and sorry for the noob question