The correct tire pressure will be stamped on the sidewall of the tire, listed as "maximum pressure". This is what it should be inflated to, all the time.
Underinflated tires will wear on both inner and outer edges. The most common problem on inner edge wear is a loose wheel bearing.
2012 Jay Flight 19RD
2010 Tundra TRD DBL Cab
1 Spoiled Dog