Rim Offset for a nissan frontierq

Ok now I know i got an answer in mm but I am wondering about inches. I was looking at most wheels and they do it in inches so a +40mm offset is what 4 inch offset? I was looking at some wheels and it has 4.125 and 4 and 4.5 backspacing i remember a long time ago to get the largest back spacing however what do i need for the frontier? will a 4 inch on a 7 inch wide rim work? or do i need the 4.5 i am lost....

What width are your wheels? Here is an equasion to figure out backspacing.

Backspacing = ((rim width + 1")/2)+(mm offset/25.4)

ex: if you have a 7" wheel with a 40mm offset your back spacing would be 5.57"

5.57 = ((7+1)/2)+(40/25.4)

for an 8.5" with 40mm I assume you are looking at.

Backspacing would be 6.32"

ya we did those 20x8.5 wheels on my bros frontier and they had a 45mm offset. They tucked nice.