A nice little tool that will help you calibrate your feed rate and To use this lay the filament in the line running the length of the tool. Make a mark on the filament at the cross hatch (Short side away from printer). Extrude 100mm of filament, the mark should lay in the cross hatch. If it does not use this formula.
N=O•(100/A)

N= New Steps/mm O=Old Steps/mm A=Actual Steps/mm

If a simplified version of this tool is desired let me know in comments and Ill create one