http://designerstoolbox.com/designresources/postcards Designers Toolbox: Postcard Sizes standard postcard sizes http://designerstoolbox.com/designresources/postcards standard postcard sizes Designers Toolbox: Postcard Sizes 21. Designers Toolbox: Postcard Sizes Designers Toolbox Designers Toolbox: Postcard Sizes 21. Designers Toolbox: Postcard Sizes