Thanks to the video below. This is the easiest way to calibrate e-steps for a bowden tube system.

Here are the step by steps

Heat up the nozzle

Unscrew the thread or remove the PTFE tube right after the extruder

Snip the filament

Set the extruder to extrude 100mm

Snip the extruded filament and measure it

Take the measurement and use this formula

old_value * 100 / measurement

Retrieve the old value from the printer either by checking the LCD panel or using OctoPrint with the M503 command

M503

Look for “Steps per unit”

After using the formula, store the new value using the LCD or OctoPrint

For OctoPrint, you can store the settings with the command below (this sets it to 96.4)

M92 E96.4


How to Calibrate E steps on a Direct Drive 

Measure from the filament entry point up to 100mm and mark with a sharpie. Measure another 20mm up and mark with a sharpie. Heat up the nozzle and extrude 100mm. Measure the distance from the extruder to the sharpie mark. Do the calculation based off 100mm to get your new value. Then, enter the values into the TH3D calculator - https://www.th3dstudio.com/estep-calculator/