What Size Poly Bag Do I Need for My Box?

Are you wondering what size poly mailer is right for your products or boxes? Choosing the wrong size can lead to higher shipping costs, product damage, and frustrated customers. In this complete guide, you’ll learn how to pick the perfect poly mailer size based on your product dimensions, shipping goals, and industry best practices.

📦 What Are Poly Mailers?

Poly mailers are durable, flexible plastic mailing envelopes made from polyethylene. Lightweight yet tear-resistant, these mailers are the go-to choice for e-commerce retailers shipping non-fragile goods like clothing, accessories, and supplements.

Key Benefits:

  • Lightweight to reduce shipping costs

  • Waterproof and tear-resistant

  • Flexible for odd-shaped or soft goods

  • Self-sealing for quick packing

Ideal for shipping:
✔ T-shirts, leggings, and casual apparel
✔ Books and magazines
✔ Jewelry and accessories
✔ Soft goods like towels and linens

📐 Poly Mailer Sizes Chart: What Size Poly Bag Fits Your Product?

Poly mailers come in standard sizes that accommodate everything from small accessories to bundled clothing items. Here’s a quick reference chart to help you select the best size:

Size Category External Dimensions Usable Space Best For
Small 6” x 9” 5.75” x 9” Jewelry, small electronics
9” x 12” 8.75” x 12” Books, accessories, documents
Medium 10” x 13” 9.75” x 13” Shirts, blouses
12” x 15.5” 11.75” x 15.5” Multiple clothing items
Large 14” x 17” 13.75” x 17” Jeans, jackets, thick garments
19” x 24” 18.75” x 24” Bulk apparel, large documents
Extra Large 20” x 24” 19.75” x 24” Coats, blankets, large textiles
24” x 36” 23.75” x 36” Pillows, linens, bedding

✏️ Pro Tip:

Always measure your product after it’s folded or packed, and allow for about 0.5" clearance on each side for ease of sealing.

🧮 How to Measure Your Product for a Poly Mailer

To determine what size poly bag you need, follow these steps:

  1. Measure your item: Get the length, width, and depth (thickness). Lay clothing flat for accuracy.

  2. Add buffer space: Add 0.5”–1” to each side for ease of insertion and closure.

  3. Match with usable mailer size: Use the internal dimensions, not the external, to ensure a good fit.

  4. Check weight and flexibility: If the item is rigid or fragile, a box may be better.

🚫 When NOT to Use Poly Mailers

Poly mailers are not suitable for every item. Avoid using them in the following scenarios:

  • Fragile items like glassware or electronics

  • Bulky or rigid products that won’t conform to the envelope shape

  • High-value goods that need tamper-proof packaging

  • Stacked or boxed items that require structure

Alternatives:

  • Corrugated boxes for protection

  • Padded envelopes for small fragile items

  • Rigid mailers for documents and photos

🧠 Why Poly Mailer Size Matters

1. Avoid Product Damage

An undersized mailer risks tearing; an oversized one allows too much movement.

2. Lower Shipping Costs

Using a poly mailer that’s just the right size minimizes dimensional weight (DIM weight), which shipping carriers use to calculate cost.

3. Professional Look

A well-sized mailer makes your brand appear polished and eco-conscious by reducing waste and excess packaging.

📦 When to Use Poly Mailers: Best Use Cases

Poly mailers are ideal for:

  • E-commerce fashion brands shipping casual or folded apparel

  • Subscription boxes with soft or lightweight items

  • Retailers of supplements or soft-packaged goods

  • Merch sellers shipping items like hats or t-shirts

Why choose poly mailers?

  • Faster packing process

  • Less storage space required

  • Environmentally friendly options available

  • Often cheaper than boxes

✨ Bonus: How to Simplify Fulfillment with a 3PL

Tired of figuring out logistics yourself?

Partner with a trusted third-party logistics provider (3PL) like eFulfillment Service. They’ll handle storage, packing, and shipping—while helping you choose the perfect poly mailer size every time.

🔚 Final Thoughts: Find the Perfect Poly Mailer Size for Every Product

Choosing the right poly mailer size isn’t just about fitting a product inside a bag—it’s about cost savings, customer satisfaction, and efficient shipping operations.

✅ Quick Recap:

  • Measure your product carefully

  • Match it to the right mailer based on usable space

  • Avoid over- or under-sizing to prevent damage and save on shipping

  • Use boxes for fragile, rigid, or high-value items

Whether you’re shipping one t-shirt or a stack of linens, using the proper poly mailer can boost your brand’s professionalism while keeping your bottom line in check.

Back to blog