Post office mailing envelope sizes

Here are the standard mailing envelope sizes accepted by the United States Postal Service (USPS):

Letter Envelopes

• 6 3/4: 6 1/8 x 3 5/8 inches (15.5 x 9.2 cm)

• 6 1/2: 6 1/2 x 3 1/2 inches (16.5 x 8.9 cm)

• 6: 6 1/2 x 3 5/8 inches (16.5 x 9.2 cm)

Large Envelopes

• Large Flat Rate Envelope: 12 x 15 1/2 inches (30.5 x 39.4 cm)
• Large Envelope (Greeting Card Size): 5 1/2 x 8 3/4 inches (14 x 22.2 cm)
• Large Envelope (Catalog Size): 6 1/2 x 9 1/2 inches (16.5 x 24.1 cm)

Flat Rate Envelopes

• Small Flat Rate Envelope: 9 1/2 x 4 1/2 inches (24.1 x 11.4 cm)
• Medium Flat Rate Envelope: 11 x 6 1/8 inches (27.9 x 15.5 cm)
• Large Flat Rate Envelope: 12 x 15 1/2 inches (30.5 x 39.4 cm)

Specialty Envelopes

• Square Envelope: 6 1/2 x 6 1/2 inches (16.5 x 16.5 cm)
• Long Envelope: 9 1/2 x 4 1/2 inches (24.1 x 11.4 cm) or 11 x 6 1/8 inches (27.9 x 15.5 cm)
• Oversized Envelope: varies in size, but typically larger than 12 x 15 1/2 inches (30.5 x 39.4 cm)

Please note that these sizes are subject to change, and it's always a good idea to check with the USPS for the most up-to-date information on mailing envelope sizes.