How to Measure Poly Bags for Shipping: A Step-by-Step Guide

The moment a product is packed, its fate is sealed—literally. If the packaging isn’t the right fit, the product becomes vulnerable as it moves through the shipping process. By the time it reaches the customer, it could be damaged—leading to returns, disappointment, and lost revenue.

A common culprit in these issues is improper poly bag sizing. But, with the right measurements, you’ll never have to worry about your products reaching their destination in less-than-pristine condition. 

Why Accurate Poly Bag Sizing Matters 

Even a small difference in poly bag size can significantly impact product shipping protection. For example, a glass bottle in a bag that's slightly too large could shift during handling, leading to cracks or breakage. If the bag is too small, pressure could cause deformation or punctures, especially for fragile items. These minor sizing issues can quickly result in costly returns and dissatisfied customers.

Improper poly bag sizing also affects efficiency. Oversized bags leave extra space, raising shipping costs since carriers charge based on volume or weight. On the other hand, bags that are too small can slow packing times as employees struggle to fit items in or add extra padding. In some cases, products may need to be re-packed to meet shipping standards and the requirements of selling platforms, adding unnecessary labor and causing delays.

That’s why it’s critical to learn how to measure poly bags for shipping. By ensuring accurate poly bag sizing, you can minimize costs, streamline packing, meet platform standards, and deliver a better customer experience.

Measuring Poly Bags for the Perfect Fit 

Poly bags come in various types, each requiring a unique measuring approach. Note that in North America, dimensions for poly bags are typically presented as Width × Length × Depth (or Gusset). However, it’s always a good idea to confirm with your supplier to ensure consistency. 

Let’s break it down.

1. Flat Poly Bags

Flat poly bags, or layflat bags, are single-layer plastic bags with no gussets or extra folds. However, this type of packaging may also include features like extended lips for easy handling, headers for labeling or sealing, and perforations for easy dispensing.

These versatile bags come in different sealing styles:

• Standard flat bags: Sealed along the sides and bottom for general-purpose use.
• Sideweld bags: Heat-sealed along the vertical sides with a folded bottom for a clean, lightweight design, often used in retail.
• Bottom seal bags: Reinforced with a strong heat seal along the bottom for heavier or bulkier items.

How to Measure a Flat Poly Bag

1. Lay the bag flat.
   Place the bag on a smooth surface, smoothing out wrinkles or folds. For bags with an extended lip or header, exclude the header from the measurement.
2. Measure the width.
   Measure across the opening from one outer edge to the other, ensuring the bag is completely flat. Fully account for any seals or folds when measuring the width.
3. Measure the length.
   Measure from the top edge of the usable portion (just below the opening) to the bottom edge. Include any sealed areas as part of the length.

 

2. Gusseted Poly Bags

Gusseted poly bags, commonly used for food packaging, industrial supplies, or as liners for boxes and pallets, feature expandable panels that provide extra space for bulky or oddly shaped items. Depending on the design, these gussets can be located on the sides, bottom, or both, offering flexibility for various applications.

How to Measure a Gusseted Poly Bag

1. Identify the gusset type.
   Check if the bag has side gussets (on both sides), a bottom gusset (at the base), or both. 
2. Measure the width.
   Flatten the bag completely, then measure from one outer edge to the other. If there are side gussets, make sure they’re unfolded.
3. Measure the length.
   Lay the bag flat and measure from the top (where it opens) to the sealed bottom edge.
4. Measure the depth.
   In gusseted bags, “depth” refers to the front-to-back poly bag dimension created by the gussets. Expand them fully and measure accordingly.
   
   Note that when measuring the depth of side gussets, measure across one side panel and double that figure (for example, 3 inches on each side totals 6 inches). If the poly bag features a bottom gusset, just measure across the fully expanded bottom panel, from one edge to the other.

 

3. Resealable Poly Bags

Also called zipper or reclosable bags, these are similar to flat bags but feature a closure mechanism like a zipper or adhesive strip for multiple uses. They’re great for keeping items fresh, secure, and protected from moisture and contaminants.

How to Measure a Resealable Poly Bag

1. Prepare the bag.
   Close the zipper or seal to ensure accurate measurements. Lay the empty bag flat on a smooth surface, smoothing out any air pockets or folds. If the bag has gussets, fully expand them before measuring to capture the correct poly bag dimensions.
2. Measure the width.
   Measure from one outer edge to the other, including any folded gusset sections if any. Ensure the zipper lies flat so it doesn’t add extra bulk to your measurement.
3. Measure the length.
   Start just below the zipper and measure to the sealed bottom using a measuring tape.
4. Measure the depth (if gusseted).
   If the bag has a gusset (bottom or side), fully expand it and measure across the gusseted section. For side gussets, measure one side and double it for total depth.

 

4. Wicketed Poly Bags

Wicketed poly bags are a smart choice for fast, efficient packing. They’re designed for easy dispensing, thanks to the way they’re grouped at the top. Most are attached to a metal wicket, but some variations, like staple-pack poly bags, use staples instead. You’ll also find gusseted versions for bulkier items.

How to Measure a Wicketed Poly Bag

1. Remove the bag.
   If it’s a standard wicketed bag, slide one off the metal wicket carefully to avoid tearing the lip or the holes. For staple pack bags, tear off a bag cleanly from the staples at the top.
2. Measure the width.
   With the bag spread out flat, measure from one side to the other across the opening. If the bag has gussets, make sure they’re expanded so you get the full width.
3. Measure the length.
   Lay the bag flat and measure from the sealed bottom up to the base of the lip—the section with the holes or staples. Since the lip isn’t part of the usable space, leave it out of this measurement.
4. Measure the lip or header.
   For standard wicketed bags, the lip or header is the portion at the top that contains the holes. Measure from the base of the opening to the top edge where the holes are. For staple pack bags, measure the length of the stapled section at the top. This ensures the bags will fit properly on your dispensing system.

Picking Your Measuring Tools

For more complex bag styles like gusseted bags, a flexible measuring tape is ideal because it conforms easily to folds and curves. For simpler formats—such as flat, resealable non-gusseted bags, or wicketed bags—a ruler or caliper can provide precise width and depth measurements.

If you’re unsure about which tool or method to use, many poly bag suppliers offer sizing guides with detailed charts. These are typically available on their websites or can be requested directly from the manufacturer, ensuring you select the right size for your products every time.

 

Determining the Right Poly Bag Thickness

Choosing the right poly bag thickness is essential for protecting your products and meeting platform requirements. Measured in mils (1 mil = 0.001 inches), the appropriate thickness depends on the item's weight, size, and fragility. 

Lightweight items like clothing typically need 1-2 mils, medium-weight or slightly sharp items require 3-4 mils, and heavy or sharp-edged items benefit from 5-6 mils for added durability. If your bag will be stacked or exposed to pressure during shipping, factor in the compression risk when measuring and choose thicker bags (4-6 mils) to handle additional stress.

To make sure your bags are up to the task, you can rely on pre-tested bags with supplier-provided specifications for tear strength and puncture resistance. You can also verify thickness yourself with a micrometer for accuracy, especially for Amazon or Walmart standards. A micrometer offers precise thickness measurements to the nearest 0.001 inches.

How to use a micrometer:

• Lay the bag flat to avoid folds or seams.
• Position the material between the micrometer’s anvil and spindle.
• Tighten gently and read the measurement on the display or scale.

In addition to precise measurements, hands-on checks help confirm a bag’s performance. Filling the bag with the product, lifting it to check its strength, or testing the seal’s reliability ensures it can handle packing and shipping demands.

Find the suitable poly bag and poly bag thickness for your product with this quick guide:

Note: Some poly bag types, like resealable bags, may come in a wider range of thicknesses, especially when intended for products requiring a higher level of protection, like food or hazardous materials.

Expert Tips for Measuring Poly Bags  

Improve the accuracy of your poly bag measurements with these practical tips:

1. Measure the product first.
   Start by measuring the product’s length, width, height, and any irregularities in shape. The results will constitute the poly bag dimensions, which will form the baseline for selecting the right bag poly bag size.
2. Account for extra space.
   Add a buffer to your measurements to ensure the product fits comfortably without straining the bag, especially for fragile or irregularly shaped items.
3. Account for the opening size.
   Ensure the bag’s opening is wide enough for the product to slide in easily. Add extra width if the item has sharp edges or bulky features to prevent tearing during packing.
4. Allow for expansion (for gusseted bags).
   For gusseted bags, measure the gusset’s full expansion to ensure it accommodates the product’s size and shape without packing delays.
5. Check for consistency.
   Manufacturers may have slight size variations in their production. Measure several bags from the same batch to ensure they are uniform in size and meet your product’s requirements.
6. Check bag seals.
   Ensure heat-sealed bags have strong, even seals. A poor seal can affect the bag's usable length and compromise product protection.
7. Use proper closure methods.
   For resealable bags, test the zipper or adhesive strip to ensure it doesn’t interfere with the bag’s opening or usable dimensions.
8. Consider the product’s shape.
   Irregularly shaped products may require a larger bag to avoid compression or damage. Account for this when measuring and selecting the poly bag size.
9. Avoid overstuffing.
   Never force a product into a bag, as overstuffing can distort the bag, damage the product, and make measurements unreliable.

Armed with these tips, you're all set to find the ideal poly bag sizes—and Supply Legends is here to make that process easier than ever.

Precise Poly Bag Sizing Starts with Supply Legends

Your business deserves poly bags that deliver every time, and Supply Legends get that. Whether it’s for small items, like jewelry or electronics, or for bulkier goods, such as apparel or industrial tools, we have an extensive selection of poly bag sizes for your diverse packaging needs. 

On top of that, our Amazon- and Walmart-compliant bags are crafted to meet stringent marketplace standards, ensuring your products stay secure and shipping-ready.

Built for reliability and toughness, our bags handle shipping demands without inflating costs. Add in bulk discounts and lightning-fast free shipping, and you’ve got a partner that takes the guesswork out of packaging. No compromises, no gimmicks—just poly bags that fit the way they should.

Let Supply Legends help you size it right—contact us today.