There isn’t one pixel size that works for everyone because there are at least 2 variables: software resolution & hardware. Either can make a TREMENDOUS difference in how much physical space 1 pixel takes up. You have to use your own personal settings based on 1) the image resolution; 2) the application you’re printing from; & 3) the printer drivers you’ve installed.
Try creating a series of concentric B&W rings in MSPaint (or some other simple image editor), saving it as a .BMP and as a .JPG, then using your printing application to send the image to paper. Then use a ruler to see which ring is closest to the size of your disk’s printable area, and find out that ring’s diameter in pixels.