Flat mailing sizes for envelopes

Here are the standard flat mailing sizes for envelopes in the United States:

Letter Envelopes

• 3 1/2: 6 1/8 x 3 5/8 inches (15.5 x 9.2 cm)

• 4: 6 1/2 x 3 3/4 inches (16.5 x 9.5 cm)

• 5: 6 5/8 x 3 7/8 inches (16.8 x 9.8 cm)

• 6: 6 3/4 x 4 inches (17.1 x 10.2 cm)

Large Envelopes

• B4: 9 1/2 x 4 1/2 inches (24.1 x 11.4 cm)
• B5: 9 3/4 x 4 3/4 inches (24.8 x 12.1 cm)
• B6: 10 x 5 inches (25.4 x 12.7 cm)
• B7: 10 1/2 x 5 1/2 inches (26.7 x 14 cm)

Flat Envelopes

• Flat 1: 11 x 6 inches (27.9 x 15.2 cm)
• Flat 2: 11 1/2 x 6 1/2 inches (29.2 x 16.5 cm)
• Flat 3: 12 x 7 inches (30.5 x 17.8 cm)
• Flat 4: 12 1/2 x 7 1/2 inches (31.8 x 19.1 cm)

Specialty Envelopes

• Catalog Envelope: 12 x 9 inches (30.5 x 22.9 cm)
• Tabloid Envelope: 11 x 17 inches (27.9 x 43.2 cm)
• Legal Envelope: 8 1/2 x 14 inches (21.6 x 35.6 cm)

Please note that these are standard sizes, and some mailers may offer custom sizes or variations. Additionally, some sizes may be more suitable for certain types of mail, such as catalogs or legal documents.