About a year ago I attempted to work out the motor vehicle establishment of the German Army in September 1939 using the info on Leo Niehorster's website plus some source documents he sent to me.
The 85 1st to 4th Wave infantry divisions in the German Army in September 1939 had a combined establishment of 432,515 horses (210,430 light draught, 78,291 heavy draught and 143,794 riding).
They also had a total establishment of 114,799 motor vehicles (31,653 personnel carriers, 41,090 load carriers & prime movers, 147 armoured cars and 41,909 motor cycles).
If they had all been motorised infantry divisions they would have had a total establishment of 342,380 motor vehicles (84,065 personnel carriers, 143,395 load carriers & prime movers, 2,550 armoured cars and 112,370 motor cycles) and no horses.
That's a difference of 227,581 motor vehicles (52,412 personnel carriers, 102,305 load carriers & prime movers, 2,403 armoured cars and 227,581 motor cycles) and 432,515 horses.
A German motorised infantry division (of which there were four) had 4,028 motor vehicles and no horses. A standard 1st Wave infantry division (of which there were 23) had 1,539 motor vehicles and 4,842 horses. So the exchange rate is about 2.5 ordinary infantry divisions for one motorised division. Except that it isn't as simple as that.