What is the minimum paper weight for USPS postcard printing?

[RonPella]

I'm going to be printing some postcards on my color copier - what is the minimum paper weight that the USPS will accept to print on for mailing postcards?

[Jeff]

I believe it is paper thickness not weight that is regulated.

According to http://pe.usps.com/Archive/HTML/DMMA....htm#wp1002733 minimum thickness for a USPS postcard is 0.007" and maximum thickness is 0.016"

Typical coated cover stock thickness is:
80 lb .008
100 lb .010
110 lb .011
120 lb .012

100 lb cover (270 gsm) is probably the most popular thickness for postcards. However you may find your color copier doesn't support stock this thick, in which case 80 lb cover (215 gsm) should be fine in terms of the postal regulation for postcard thickness.

[Jeff]

Note also that uncoated paper will typically be less dense, higher bulk more thickness per weight, than a smooth finish coated paper, so if the postcard is a relatively simple low-ink (or low-toner in your case) that can use a cheaper uncoated stock you may get by with a lighter but equally thick uncoated cover stock.

Uncoated vellum finish cardstock thicknesses are typically:
65 lb .009
80 lb .0105
100 lb .0135

vs. coated cover stock
80 lb .008
100 lb .010