N gauge is 1:148 - 1:160 scale.
See:
N scale - Wikipedia, the free encyclopedia
Thus a 6.5 foot door could be .53 inch to 0.49 in N gauge.
1/2" is a good approximation.
5/8" is 0.62 inch which is slightly large for N scale but probably close enough.
A 6.5' door is 0.90" inch in 1/87 scale.
7/8" = 0.88" which is close.
1 1/8 inch sounds a little large for 1/87 scale.