This is the one I use, but theres a lot of them online. I have the calculation rate for steps per minute to characters per hour in my post
Again though I would be careful. I remember you saying you mined like 1500+ sentences in the past few weeks recently, and I didn’t start reading speed practice till i was consistently mining less than 30 words per book for the stuff I was reading. I think you’re probably at the stage where you still have a lot of speed to gain purely from getting more familiar with the content and trying to go fast may do more harm than good.