What Size Mailing Bag Do I Need? UK Grey Mailing Bag Guide for 2026

Every week we help UK sellers on marketplaces like eBay, Amazon, Vinted and Shopify choose the right grey mailing bag sizes for their products. Guessing mailing bag sizes used to be normal. Many UK sellers still line up a parcel next to a stack of grey bags and hope for the best. In 2026, that guesswork costs real money. Postage is higher, couriers rely more on scanners, and customers expect neat, well-fitted parcels that are easy to return if needed.

At Mr Bags, we work with clothing brands, marketplace sellers, warehouses and small shops across the UK. Grey mailing bags are one of our most popular products. This guide explains which size grey mailing bag to use for different items, how sizing affects postage, and how to choose the right bag first time, every time.

What Are Grey Mailing Bags and Why Do UK Sellers Use Them?

Grey mailing bags are lightweight plastic posting bags with a self-seal strip. They are waterproof, tear-resistant and opaque, so they keep contents hidden and protected during delivery. You can see our full range here: Grey Mailing Bags and our wider range of colours and sizes here: Mailing Bags.

Most UK eCommerce brands use grey mailing bags for:

• Clothing and fashion orders
• Books, media and gifts
• Soft home textiles such as towels and bedding
• Non-fragile boxed goods that need moisture protection

Grey remains a favourite because it looks professional, matches most brand styles, and gives strong privacy. For colour-led brands, there are also coloured options such as Blue Mailing Bags, Green Mailing Bags, Pink Mailing Bags and Purple Mailing Bags.

Why Mailing Bag Size Matters More in 2026

Choosing the right size is not just about making the parcel look tidy. In 2026 it affects:

• Postage costs: larger bags can push parcels into a higher price band.
• Courier handling: automation prefers compact, well-filled parcels.
• Damage risk: too much empty space lets items move and crease.
• Returns: poor fit leads to bent boxes, crushed items and complaints.
• Environmental impact: oversized bags use more material than needed.

Grey Mailing Bag Size Chart – Full UK Range

Below is a clear size chart for our grey mailing bag range. The “Typical items” column is based on real orders and feedback from UK sellers.

Best Grey Mailing Bag Sizes for Clothing

Clothing is where most sellers struggle with sizing. Here is a simple breakdown using the most common garment types.

• Single T-shirt: 9×12" for light tees, 10×14" for thicker fabrics or oversized styles.
• Light jumpers and cardigans: 10×14" is usually enough when folded neatly.
• Standard hoodie: 12×16" works for most adult hoodies.
• Hoodie and joggers set: 13×19" gives comfortable room for a full tracksuit.
• Jeans: most adult jeans fit well in 12×16". Slim styles may fit 10×14".
• Jackets: 14×21" suits most light and midweight jackets.
• Coats and heavy outerwear: 15×18" is better for thicker winter coats.
• Children’s bundles: 10×14" or 12×16", depending on age and number of pieces.
• Large apparel bundles: 13×19" or 15×18" for multi-garment orders.

For many brands, the real workhorses are the 12×16" and 13×19" sizes. You can find them here for quick reordering: Grey Mailing Bags 12×16" and Grey Mailing Bags 13×19".

Mailing Bag Sizes for Non-Clothing Items

Grey mailing bags are also used for many non-clothing items. Below are simple size suggestions:

• Small tech accessories: 4.5×7" or 6.5×9" for cables, small cases and spares.
• Books and media: 9×12" for thin paperbacks, 10×14" for thicker books or small bundles.
• Gifts and boxed cosmetics: 9×12" or 10×14" depending on box size.
• Soft toys and plush: 12×16", 13×19" or larger if needed.
• Fabrics and textiles: 14×21", 15×18" or 17×24" depending on thickness.
• Bedding sets and throws: 17×24", 20×26" or 21×24".
• Large boxed items and wholesale packs: 24×36", 28×30" or 28×34".

For fragile items, we recommend using a box inside the bag. You can view our Cardboard Boxes range for that extra layer of protection.

Royal Mail Small Parcel and Grey Mailing Bags

Royal Mail Small Parcel (at the time of writing) allows parcels up to 35 × 25 × 16 cm. Many grey mailing bag orders are designed to stay inside this band for clothing and soft goods.

In general:

• 9×12", 10×14" and 12×16" bags fit well within Small Parcel bands for most clothing.
• 13×19" can also fit if the item is folded flat and not overfilled.
• Larger sizes such as 17×24" and above may move into higher bands depending on contents.

Always check how thick the parcel becomes after packing. A soft hoodie in a 12×16" bag will normally stay flexible enough for Small Parcel. A rigid shoebox, however, may be better in a box sent as a different band.

How Couriers Handle Mailing Bag Sizes in 2026

Most major UK couriers now use cameras, belts and scanners to move parcels. Poorly packed mailing bags cause problems if they catch on equipment or if the size is far larger than the item inside.

• Royal Mail: favours neat, flatter parcels that stack easily in bags and cages.
• Evri: uses a lot of automated sorting, so compact, regular shapes travel better.
• DPD: strong focus on accurate dimensions. Oversized bags around small items can be flagged.
• UPS and other couriers: work best with well-filled bags or boxed items inside the mailing bag.

For peace of mind with heavier or more valuable orders, many brands now use a smaller box and then place it inside a grey mailing bag. This keeps labels clean and protects the box from scuffs.

Packaging Trends in 2026: Why Sizing Accuracy Matters

In 2026, three trends are pushing UK sellers to tighten up their packaging sizes:

• Rising postage costs: every extra centimetre of wasted space can add up across thousands of orders.
• Automation: more parcels are scanned, weighed and measured automatically, so oversizing is harder to hide.
• Environmental pressure: customers notice when a tiny item arrives in an oversized bag, and many now call it out.

Choosing the right mailing bag size is one of the easiest improvements a seller can make. It saves money, reduces waste and looks more professional.

Why Sizes Differ Between Suppliers

If you compare our grey mailing bags with other suppliers, you may notice some differences in how sizes are listed. Common reasons include:

• Some list the size including the flap, others do not.
• Some measure from the inside, others from the outside edge.
• Film stretch and tolerances can change the final fill size slightly.

At Mr Bags we label sizes clearly and provide real-world usage examples, so you can match items to bags with confidence. If in doubt, size up once rather than once too small.

How Mailing Bag Size Affects Postage Cost

Postage in 2026 is driven by both weight and size. Most soft clothing items are light enough that the size of the bag is the main variable. Oversizing can cause:

• Parcels to move into a higher Royal Mail band.
• Extra handling surcharges with some couriers.
• More returns due to damaged or bent contents.

As a rough guide, pick the smallest bag that allows the item to slide in without stress on the seal or obvious stretching. If you find yourself folding the same item differently every time, that usually means you are between sizes and should standardise on the larger of the two options.

How to Fold Clothing for the Smallest Possible Mailing Bag

A good folding method can often allow you to drop down one bag size, especially for hoodies and jumpers. A simple approach is:

• Lay the garment flat and smooth out creases.
• Fold sleeves inwards so they sit within the body width.
• Fold the garment vertically into thirds or halves, depending on length.
• Press out air lightly as you fold.
• Check against the opening of the bag before sliding it inside.

Many brands find that, with consistent folding, a hoodie that felt like it needed 13×19" can reliably fit into 12×16", saving material and postage space across the whole year.

Simple Buyer’s Guide: How to Choose the Right Mailing Bag Size

Here is a quick process you can use in your office or warehouse when picking sizes for the first time:

1. Measure the item when folded as you plan to pack it (length, width and approximate thickness).
2. Compare the folded size to the chart above and add around 2–3 cm of allowance each way.
3. Choose the smallest bag that gives a smooth fit without stretching the film.
4. Test-pack a sample order and check if it still fits once labelled.
5. Record the final size choice as a standard for that SKU or product type.

Once you map garments and product types to specific bag sizes, your packing team can work much faster and new staff can train more easily.

Common Mistakes to Avoid with Mailing Bag Sizes

Some of the most common sizing mistakes we see from UK sellers include:

• Choosing a bag that is just too small: this stresses the seal and can cause tearing at the corners.
• Using very large bags for small items: contents move around, labels crease and customers feel packaging is wasteful.
• Not thinking about returns: if customers re-use the bag, a tight fit can make resealing difficult.
• Ignoring weight and value: heavy or higher-value items often need a box as well as a bag.
• Skipping tape on heavy parcels: even with a good self-seal, many sellers add extra Packaging Tape for support.

Retail vs Business vs Warehouse: Different Size Needs

Not every buyer needs the same grey mailing bag mix. A small Depop or Vinted seller has different needs from a fashion warehouse or fulfilment centre.

• Casual sellers and side hustles: a few core sizes such as 9×12", 10×14" and 12×16" usually cover most orders.
• Small online shops: often add 13×19" and 14×21" for hoodies and jackets, plus a few 6.5×9" bags for accessories.
• Growing brands and warehouses: may stock the full size range from 4.5×7" up to 24×36" and beyond for textiles and bulk orders.

If you are planning a switch to standardised sizes, our team can help you choose a core set that balances efficiency with flexibility. Start by reviewing your main product types, then map each to a short list of grey mailing bag sizes.

Environmental Impact of Correct Mailing Bag Sizing

Correct sizing is not just good for costs. It also reduces waste. A smaller, well-fitted bag uses less plastic than an oversized alternative and often means fewer extra fillers such as paper or bubble wrap.

For some items, a poly mailing bag is not needed at all. Flat, dry, low-risk goods may be better in Paper Bags or gift-style packaging. Where you do choose plastic mailing bags, accurate sizing reduces the total material used across the year.

Internal Packaging Combinations That Work Well

Many UK sellers use a simple packaging kit built around grey mailing bags, for example:

• Grey mailing bags for main shipping protection.
• Cardboard Boxes for fragile or high-value items placed inside a bag.
• Packaging Tape to reinforce heavy parcels or seal boxes.
• Party Bags or small gift bags inside parcels for branded touches.

Brands that want to bring more colour into their packaging often combine grey mailing bags with coloured options such as Blue, Green, Pink or Purple Mailing Bags, using grey as the main workhorse size and colours for launches or special ranges.

Summary: Getting Mailing Bag Sizes Right in 2026

Grey mailing bags remain one of the most efficient ways to send clothing, textiles and soft goods across the UK. By matching each product type to a clear size, you can cut packing time, keep postage under control and offer a neater unboxing experience for customers.

Start with a core set such as 9×12", 10×14", 12×16" and 13×19", then add larger sizes as your range grows. Build simple rules for your team, test a few sample orders and review your choices regularly as your product mix changes.

You can explore the full grey range here: Grey Mailing Bags Collection, or view all options in our main Mailing Bags category. At Mr Bags we stock every grey mailing bag size from 4.5×7 inch up to 28×34 inch, so you can standardise your sizes and keep reordering simple.

Our Service Guarantee

• 5★ rated service on Trustpilot.
• Fast UK delivery with reliable couriers.
• Same-day dispatch cut-off on qualifying orders.
• Bulk and trade support for growing brands and warehouses.
• Email and message support from a friendly UK-based team.

Useful Downloads

These helpful downloads give you quick, ready-to-use tools for choosing the right mailing bag sizes and planning bulk orders.

• Mr Bags – Mailing Bags Size Guide (PDF)
• Mr Bags – Bulk Order Form (PDF)
• Royal Mail Size and Weight Guide