Backspacing vs Wheel Spacers

Does anyone know how to calculate the approximate backspacing or offset change if running a 0 offset or -12 offset wheel with spacers vs running something like an SCS wheel with 3.5 BS and -32 offset. Trying to get as close to SCS specs as possible. Not willing to wait until they come back into stock. Have new 35s sitting at home and I'm on stock wheels with 1.5" spacers now

 

https://www.tacomaworld.com/threads/wheel-backspacing-and-offset-info.102992/

 

https://www.rimsntires.com/specspro.jsp

A good site to compare offsets of what you are running vs what you are looking at

 

offset is from the center of the wheel to the centerbore, back spacing is from the back of the wheel to centerbore/where the wheel connects to your truck. if you're looking for poke try to match up the back spacing

 

8" wide, 0 offset and 1.25" wheel spacer=-32mm offset, 3.25" backspace