Editing Paper size (section)

=== Envelope sizes ===

{| class="wikitable"
|+ US envelopes<ref name="PWG"/>
! Name !! inch × inch !! mm × mm !!title="aspect ratio"| AR
|-
! Personal
| {{size|3+5/8|6+1/2|in|mm|ar=on}}
|-
! Monarch
| {{size|3+7/8|7+1/2|in|mm|ar=on}}
|-
! A2
| {{size|4+3/8|5+3/4|in|mm|ar=on}}
|-
! #9
| {{size|3+7/8|8+7/8|in|mm|ar=on}}
|-
! #10, Commercial
| {{size|4+1/8|9+1/2|in|mm|ar=on}}
|-
! #11
| {{size|4+1/2|10+3/8|in|mm|ar=on}}
|-
! #12
| {{size|4+3/4|11|in|mm|ar=on}}
|-
! #14
| {{size|5|11+1/2|in|mm|ar=on}}
|}
<!--PWF5101.1: 6x9, 7x9, 9x11, 9x12, 10x13, 10x14, 10x15-->

{| class="wikitable"
|+ US Postal Service size limitations, height × width × thickness<ref>{{cite book |publisher=United States Postal Service |url=http://pe.usps.com/text/dmm300/101.htm#6_3_1 |title=DMM 101: Physical Standards |archive-url=https://web.archive.org/web/20140426235609/http://pe.usps.com/text/dmm300/101.htm#6_3_1 |archive-date=26 April 2014 |chapter=Section 6.3.2: Postcard Dimensions |access-date=26 April 2014}}</ref>
! Mail piece
! inch × inch × inch !! mm × mm × mm
|-
!title="The minimal thickness is just 0.007-inch if the shorter side does not exceed 4.25 inches and the longer side does not exceed 6 inches."| Minimum 
| {{convert|3+1/2|x|5|x|0.009|in|mm|disp=tablecen|sigfig=3}} 
|-
! Postcard maximum 
| {{convert|4+1/4|x|6|x|0.016|in|mm|disp=tablecen|sigfig=3}}
|-
! Letter maximum 
| {{convert|6+1/8|x|11+1/2|x|1/4|in|mm|disp=tablecen|sigfig=3}}
|-
! Flat-size maximum
| {{convert|12|x|15|x|3/4|in|mm|disp=tablecen|sigfig=3}}
|}

This implies that all postcards have an aspect ratio in the range from {{resratio|20|17}} = 1.18 to {{resratio|12|7}} = 1.71, but the machinable aspect ratio is further restricted to a minimum of 1.30. The only ISO 216 size in the US postcard range is A6. The theoretical maximum aspect ratio for enveloped letters is {{resratio|23|7}} = 3.29, but is explicitly limited to 2.50.