Bubble mailers are envelopes with an interior lined with bubble wrap to protect items during shipping.
They come in a variety of sizes, each with a designated number. Here are the dimensions of the most common bubble mailer sizes:

• #000: 4" x 8"
• #00: 5" x 10"
• #0: 6" x 10"
• #1: 6" x 12"
• #2: 8" x 12"
• #3: 10" x 13"
• #4: 9 ½" x 14 ½"
• #5: 10 ½" x 16"
• #6: 12" x 15"
• #7: 14" x 19"

Please note that these are just the most common sizes, and there may be some variation depending on the manufacturer.