PLEASE NOTE PRODUCTS ARE LISTED ABOVE IN INCHES - Need help converting to centimetres? Please use this helpful table below.

Sizing Guide - Grey Mailing Bags Sizes and Order Codes

How to Measure Mailing Bags

Measuring to find out which poly mailing bag to order to fit your item(s) is easier than first meets the eye.

Simply measure the diameter of the width of the product (or products put together), by placing a tape measure under the item being packaged, and bringing the measure to top around the centre from side to side, draw the measure together and make a note of this measurement.

Then do the same for the length of the product.

Take the width measurement and divide by 2, this will provide the width measurement of the mailing bag. Then take the length measurement and do the same, to calculate the length measurement of the mailer bag.

We then match both these measurements to the nearest mailer bag measurements available, only using sizes larger to allow for movement room, otherwise it will be difficult to insert your item.

For example, a product measuring 50cm around the circumference in the middle of the shortest side, and measuring 80cm around the circumference in the middle of longest side, will fit a 25cm x 40cm mailing bag (or 10x16inch), which we then recommend that the measurements are rounded up to the nearest size available on both dimensions to ensure some movement room, so in this case, would be the 300x400cm grey mailer bag (12x16inch Mailer Bag).

Measuring the mailing bags itself to find out what size to re-order is very simple.

Measure the width from side to side (that will be the width of the mailing bag) and then measure the length from top to bottom, but not including the additional flap piece for sealing the mailing bag, as this is only included on one side, and not included in the sizes stated on our website, and referred to as the lip measurement, usually around 5cm (2inches).

Convert cm to inches

Take the cm measurement and divide by 2.5. This gives the approximate amount in inches.

For example, 75cm divided by 2.5 equals 30 inches.

Convert inches to cm

Take the inch measurement (use 0.5 for half an inch if necessary) and multiply by 2.5. This gives an approximate measurement in centimetres.

For example 30.5 inches multiplied by 2.5 equals 76.25 (76 centimetres rounded down).

What size mailing bags for clothes?

Here are some typical mailing bag sizes that suit certain clothing; a folded shirt would fit in 13x19inch mailer, a coat would fit in 24x36inch mailer, two shoe boxes would fit in our 23x28inch mailer, for an exact match, please use our handy measuring guide, How to Measure for Mailing Bags, to check the exact size of the grey poly mailer that is needed for single items of clothing, or even a bundle of clothes.

What size mailing bag for shoe box?

A standard shoe box is around 3x7x11inches and this would usually fit in a 13x19 Mailer Bag.

Two shoe boxes would usually fit in a 21x24inch Mailer Bag or 23x28inch Mailer Bag

How to check this?

Please use our handy measuring guide, How to Measure for Mailing Bags, to check the exact mailing bag size for the shoe box that is needed.

What size mailing bags for t shirts?

One single folded T-shirt would usually be folded to fit within a 12x16inch clear shirt bag for high presentation packing, therefore the size of this clear bag could be used as a guide for which grey mailing bags could be used to mail the item.

For easy to insertion and quick packing we would recommend the following:

Garments inserted in a 9x12 clear garment bags - 10x14 Mailing Bags

Garments inserted in a 10x12 clear garment bags – 12x16 Mailing Bags

Garments inserted in 12x15 or 12x16 clear garment bags - 13x19 Mailing Bags

Garments inserted in 14x17 Clear Garment Bags – 16x21 Mailing Bags

Folded Garment inserted in 15x20 Clear Garment Bag - 18x22 Mailing Bags

Single Folded Garment inserted in 18x22 Clear Garment Bag – 21x24 Mailing Bags

This then provides plenty of space for promotional materials or returns paperwork.

If clear garment bag is not being used to present the t-shirt, the fold and package the t-shirt as you would like to present and then please use our handy measuring guide, How to Measure for Mailing Bags, to check the exact size of the mailing bags needed.

What is a poly mailing bag?

Poly Mailing Bags can either be an Opaque Mailing Bags that you cannot see through, completely hiding its contents, or a Clear Mailing Bags that clearly present the contents, which is more ideal for leaflets, catalogues, and other promotional materials, so persons can see your information without even having to open the envelope.

All mailing bags have a permanent seal strip to ensure goods cannot be tampered with during transit. Some may have a printed suffocation warning notice to ensure that bag is not left with babies and children, but this is not always needed and depends on how and where the mailing bag is being used.

Poly Mailing Bags are not to be confused with Garment Bags (or Shirt Bags) used for presenting garments professionally in the e-commerce market, as these have re-sealable strip for easy opening and closing and always contain a printed suffocation warning notice on the bags, which can be an issue when mailing catalogues, as it is usually preferred the mailer has a permanent sealing strip, so this cannot be opened and the contents tampered, and in some cases the printed warning notice, can obscure the printed document contained, resulting in a poorer presentation.

Are grey plastic mailing bags recyclable?

Yes, our grey mailing bags are LDPE plastic and can recycled in the commercial situation and usually be recycled through the home domestic recycling bins or recycle centre.

However local councils all have different rules about how plastics can be recycled, so please visit your local council website to check what currently applies for household and business recycling.

Can you reuse plastic mailing bags?

Yes, they can, providing the packaging is opened carefully, without tearing the plastic the seal is adhered too. Most poly mailer packaging bags have a single sealing strip with a permanent glue, so once this seal is used to send goods initially, then it will slightly damage the grey mailer by tearing the plastic when the bag is pulled open.

However, when using the grey poly mailer bag again (say to return unwanted items on a courier) if the bag is cut carefully open, then usually there is plenty of bag left to wrap around goods and this can then be resealed together with packaging tape.

On the other hand, e commerce mailing bags often have a double sealing strip giving two permanent sealing strips, one that the sender uses to seal the package, and a second for the buyer to use when returning goods.

These custom mailers are usually printed with e-commerce shop details and a ‘cut along the dotted line’ text to ensure the buyer opens the bag in the correct place and doesn’t damage the second sealing strip for returning the goods.

For e-commerce business, it is important to ensure staff packaging goods are correctly advised to use the most outer sealing strip when packaging goods for resale, as using the inner (second strip) does result in the outer strip not being able to be used.

If bespoke printed mailers or mailing bags with double sealing strips are needed, you have further questions, or are not sure which product will work best for you, then please reach out to our friendly advisors, either on the chat box online, by emailing sales@sapphirepackaging.com or telephoning 01702 205 999. We look forward to being of assistance.




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Grey Mailing Bags

Grey mailing bags (often called grey poly mailers) are lightweight, opaque plastic shipping envelopes designed for sending non-fragile items such as clothing, soft goods, and paperwork. The grey outer layer helps conceal contents for privacy, while the plastic film provides water resistance during transit. Products in this collection are listed in inches, and the sizing table on this page provides the equivalent millimetre dimensions alongside order codes, size codes, thickness (gauge), and pack quantities.

Grey Mailing Bags — Helpful Guide

This collection focuses on opaque, self-seal mailing bags in a range of standard size codes (for example #00 through larger formats). They are commonly used for e-commerce fulfilment because they pack flat, seal quickly, and reduce volumetric space compared with cartons.

1) Opaque self-seal poly mailers (grey mailing bags)

These are the core products in this category: flexible plastic mailers with a peel-and-seal closure. The opaque grey film is intended to reduce visibility of the contents, and the plastic construction helps protect against splashes and light rain.

• Grey Mailing Bags — Opaque self-seal mailers listed by size code and order code, with a sizing guide showing inches and millimetres.

Note on thickness: Many packaging suppliers express film thickness in gauge. A commonly used conversion is microns = gauge × 0.25, meaning 220 gauge ≈ 55 microns and 260 gauge ≈ 65 microns. Thicker film generally improves puncture and tear resistance, which can be helpful for heavier or sharper-edged soft goods.

Case study: reducing packing time for apparel orders

A small apparel shipper typically spends time building cartons, taping seams, and adding void fill. Switching to correctly sized grey mailing bags can simplify the workflow: pick the smallest mailer that comfortably fits the folded garment, insert the item, remove the release liner, and seal. Because the mailer is flexible, it can reduce wasted space for soft items and can speed up packing where rigid protection is not required. The key is matching size and thickness to the product so seams are not overstressed and the closure remains clean and secure.

How to choose the correct grey mailing bag

Step 1: Measure the packed item (not the product on its own)

Measure the item after it is folded or placed in any inner packaging (such as a garment bag). Use the width and length that the mailer must accommodate, and allow extra room for the flap and for easy insertion. If your item is bulky, consider how the thickness affects the effective usable width.

Step 2: Use the size code and mm conversion table

This page includes a sizing guide that maps each order code to a size code and shows dimensions in both inches and millimetres. Use the millimetre values if you work in metric, and keep a consistent internal reference so your team selects the same size every time.

Step 3: Select an appropriate film thickness (gauge)

Film thickness is one of the main drivers of durability. As a practical guide:

• Lighter soft goods (t-shirts, thin garments): a standard gauge is often sufficient when the item has no sharp corners.
• Heavier textiles (hoodies, denim) or mixed orders: consider a thicker gauge to reduce the chance of punctures and seam stress.
• Items with edges (boxed cosmetics inside a mailer, accessories): thickness helps, but you may also need an inner protective layer or a different outer pack if crush protection is required.

Step 4: Consider privacy and presentation

Grey opaque mailers are commonly chosen when you want to reduce visibility of the contents. If you ship items where discretion matters, opacity can be as important as strength. For presentation, ensure labels adhere well and that the surface is clean and dry before applying shipping labels.

Step 5: Understand closure and tamper visibility

Self-seal closures are designed for fast packing. Once sealed, opening typically requires tearing or cutting, which can provide some visible indication of interference. However, basic adhesive closures are not a substitute for high-security tamper-evident packaging. If chain-of-custody is critical, consider packaging specifically designed and specified for tamper evidence.

Packing tips for better transit performance

• Choose the smallest practical size: Oversized mailers can allow contents to shift, increasing stress on seams and the closure.
• Keep the seal area clean: Dust, fibres, or moisture can reduce adhesive performance. Avoid overfilling so the flap can lie flat.
• Reinforce when needed: For unusually heavy soft goods, consider an inner bag or wrap to reduce abrasion against the mailer film.
• Label placement: Apply labels to a smooth area and press firmly. If you use thermal labels, confirm adhesion on plastic film in your packing environment.
• Weather exposure: Poly mailers resist splashes, but seams and closures are not designed for submersion. For high-moisture routes, consider secondary protection for sensitive contents.

Storage and handling

Store mailing bags flat in a clean, dry area away from direct sunlight and heat sources. Excess heat can affect film properties and adhesive performance over time. Keep cartons closed until use to reduce dust contamination on the seal strip.

Recycling and disposal considerations

Plastic mailing bags are often made from polyethylene-based films. Where local facilities accept plastic film, clean mailers may be suitable for film recycling streams (often via store drop-off rather than kerbside). Recyclability depends on the exact construction, inks, labels, and local rules. Remove paper labels if required by your local program and follow local guidance for plastic film.

Questions & Answers