The small 20x20 XYZ cube really doesn't work well for a print bed larger than 100x100 so I design this 100x100 XY ruler for printer that have a larger print bed.
Tighten the X and Y belt before you print this XY ruler. You need to redo the calibration again when you tighten or loose your X and Y belt next time.
1) Print this XY ruler and measure it with a caliper.
You want it to be 100mm for X and 100mm for Y. For example, I have 100.35mm for X, 100.1 for Y. I need to have the lower the steps for my X and Y to become 100mm
2) Use this formula to find the new XY steps
(Current steps x the target measurement)/the current measurement=new steps)
I'll use my Ender 3 as example.
Current steps: The default step numbers of X and Y are 80 steps/mm
Target measurement: 100mm
Current measurement: 100.35mm for X, 100.1mm for Y
In the Ender 3 menu, Control > Motion > Steps/mm
Enter 79.72 in X, 79.92 in Y
Now just save the setting (Control > Store settings) and you're done!
You can go ahead and reprint this XY ruler to check the measurement. It should be 100mm x 100mm now.