A simple 20x20x20 mm cube with a 10mm hole and 2mm chamfers and radii. Use this cube to test your printers accuracy.
If calibrating use the following equation: (20mm*current steps per mm) / actual printed cube size
e.g. 20mm x 85 steps/mm = 1700
1700 / 24mm = 70.84 steps/mm
change your steps per mm to 70.84, reprint and re measure.
N/A I used PLA