Envelopes and Postal Boxes – What Sizes Are Available and How To Choose

Forms Plus stock a wide range of packaging materials suitable for e-commerce business.  We get asked a lot about how to choose the right kind of packaging, and particularly, how to choose the size. Paying attention to the type and size of the box or envelopes you use to despatch your products can help you save money on shipping costs and reduce your company’s impact on the environment. In this blog, we’ll explain why, and help you choose the right packaging for your e-commerce business. 

Environmental Envelope and Box Considerations

Let’s look first at environmental impact. When sending out e-commerce products, there are two main areas to consider to make sure your packaging is eco-friendly.  First, you will want to look at the packaging itself. Is it fully biodegradable? Plastic free? Recycled? Recyclable?  We offer a few options.

Our Eco Postal Boxes are biodegradable, recyclable with normal household recycling and made from sustainable material that does not deplete or degrade the environment.  The cardboard used in them is sourced with FSC (Forest Stewardship Council) certification.

Enviroflute Padded Envelopes are a more environmentally friendly alternative to the traditional Jiffy Bag. Recognised as the world’s most eco-friendly padded envelope, they are fully biodegradable, plastic free, recyclable, and made from FSC accredited paper.  

Traditional, bubble-lined Padded Envelopes are another option for various items. They come in traditional gold or white, can be separated for recycling and are made using FSC accredited paper.

Secondly, choosing the right size of packaging will also help reduce your impact on the environment. Over-packaging, where a tiny item like a lipstick is either rattling around in a big cardboard box or packed in with bubble wrap or reams of paper, not only results in more waste, but burns more carbon to produce, recycle and transport. Choose the box or envelope that is the smallest size you can, and not only do you reduce wastage of packaging materials, the carbon footprint of your delivery will come down. If everyone were to do this, it would eventually result in fewer delivery vehicles on the road. 

Royal Mail Letter and Parcel Sizing

Whilst making sure your packaging is as environmentally friendly as possible, you will also want to make sure you are being efficient and saving where you can on shipping costs.

Royal Mail charges for letters and parcels according to its PiP system. This stands for Pricing in Proportion. We stock envelopes and boxes to fit four levels of PiP pricing – Letter, Large Letter, Small Parcel, and Medium Parcel.  The tables below show the internal dimensions of all our envelopes and boxes, and which Royal Mail pricing bracket they fall into.  Simply measure the product you want to ship, check its weight and order the smallest packaging option that offers the level of protection you need.

Royal Mail Large Letter packaging is ideal for sending something like a book, small fashion accessories, jewellery, flyers, or documents.  The package can be up to 2.5cm thick, so you could use a postal box or one of the larger envelopes.

Royal Mail Small Parcels are a bit bigger. These are suitable for sending clothes, shoes, or similar products. This is the preferred size for many e-commerce retailers. For bulkier items, you may need to go up to Medium Parcel. 

By using packaging that meets Royal Mail’s standard sizes, you can keep shipping costs down. If you are shipping out similar-sized items regularly, keeping to the smallest Royal Mail option will help you make substantial savings over the year. 

Other Sizing Considerations

Whilst the environment, and cost efficiency are highly significant when choosing the right packaging, protecting your product will be your ultimate goal.  The packaging should be snug, so your items do not move around inside and get damaged. It will also need to offer an appropriate level of padding and protection for your goods. You may want it to be easy to open and reseal for potential returns.

A further consideration could be how you expect your packages to ultimately be delivered. For smaller goods, many customers will prefer a letterbox sized parcel that can fit through their door, so they do not have to be home to take delivery.  UK letterboxes come in varying sizes, but the most common size is 254mm x 38mm. Anything up to a Size G in our envelope range should fit through a letterbox. E-commerce companies are now offering “letterbox flowers”, “letterbox hampers” and even, ingeniously, “letterbox wine” to ensure their clients do not miss out on deliveries!

Why is it important to choose the right size of packaging?

We have identified several good reasons for making sure you choose exactly the right size envelope or postal box. Your products will be better protected on their journey to the customer. You will save money on shipping costs. The impact of your shipping on the environment will be reduced – and you might even want to make sure you fit through their letterbox.

Use the tables below to see the full range of envelope and box sizes available from Forms Plus, and the type of packaging we have in those size.

Do get in touch if we can help you further. 

Envelope Sizes

Approx Internal SizeForms Plus Size NameSize also known asOptionsCreative UsesRoyal Mail size / weight limit
110 x 165mmSize AC6Padded White or GoldGift Cards / Place Mats / Cosmetics / JewelleryLetter
(up to 100g)
120 x 215mmSize BDLPadded White or GoldMobile Case / Cards / Cosmetics / Jewellery / BatteriesLetter
(up to 100g)
150 x 215mmSize CC5Padded White or GoldA5 Documents / Cosmetics / Cards / Photos / Purse / Wallet / StationeryLetter
(up to 100g)
180 x 265mmSize DPadded White or GoldCosmetics / Cards / Books / Stationery / Purse / WalletLarge Letter
(up to 750g)
220 x 265mmSize EPadded White or GoldCandle / Photos / Cards / Book / Craft Supplies / Chocolate / Perfume / AftershaveLarge Letter
(up to 750g)
230 x 335mmSize FC4Padded White or GoldA4 Pads / Magazines / A4 Documents / Clothing / Toiletries / Craft Supplies / BookLarge Letter
(up to 750g)
240 x 335mmSize GPadded White or GoldClothing / Craft Supplies / Toiletries / Book / Photo FrameLarge Letter
(up to 750g)
270 x 360mmSize HPadded White or GoldClothing / Craft Supplies / Toiletries / Photo Frame / MagazinesSmall Parcel
(up to 2kg)
300 x 445mmSize JPadded White or GoldCalendar / Craft Supplies / ClothingSmall Parcel
(up to 2kg)
350 x 470mmSize KC3Padded White or GoldA3 Documents / ClothingMedium Parcel
(up to 20kg)
324 x 229mmC4C4All Board or Board BackedA4 Documents / Greetings CardsLarge Letter
(up to 750g)
229 x 162mmC5C5All Board or Board BackedA5 Documents / Greetings CardsLetter
(up to 100g)
240 x 165mmC5+C5Board BackedA5 Documents / Greeting CardsLetter
(up to 100g)

Postal Box Sizes

SizeForms Plus Size NameSize also known asOptionsCreative UsesRoyal Mail size / weight limit
101 x 101mm x 20mmPostal Boxes Size 1SmallEco Postal BoxesGift Cards / Cosmetics / Jewellery / Place MatsLarge Letter (up to 750g)
163 x 112mm x 20mmPostal Boxes Size 2C6Eco Postal BoxesMobile Case / Cosmetics / Jewellery / Cards / Books / Photos / Stationery / Purse / Wallet / BatteriesLarge Letter (up to 750g)
218 x 108mm x 20mmPostal Boxes Size 3DLEco Postal BoxesCosmetics / Jewellery / Cards / Books / Photos Stationery / Purse / WalletLarge Letter (up to 750g)
225 x 160mm x 20mmPostal Boxes Size 4C5Eco Postal BoxesCosmetics / Jewellery / Cards / Books / Photos Stationery / Purse / Wallet / Gloves / HatLarge Letter (up to 750g)
202 x 143mm x 66mmPostal Boxes Size 5MiniEco Postal BoxesCandles / Photos / Cards / Books / Cosmetics / Mens Grooming / Toiletries / Stationery / Craft Supplies / Chocolates / PerfumeSmall Parcel (up to 2kg)
334 x 202 x 66mmPostal Boxes Size 7MidiEco Postal BoxesCosmetic sets / Books / Photo Frames / Hair Products / Stationery / T-ShirtsSmall Parcel (up to 2kg)
325 x 225mm x 20mmPostal Boxes Size 8C4Eco Postal BoxesT-Shirts / Magazines / CardsLarge Letter (up to 750g)
430 x 340mm x 73mmPostal Boxes Size 9MaxiEco Postal BoxesClothing / Books / Photo Frames / GamesSmall Parcel (up to 2kg)

Padded Envelopes Sizing Comparision Chart

Product CodeAroFOLFeatherpostJiffyBubble Lined BagsMail Lite
(100 x 165mm)
A (C6)
110 x 165mm
(90 x 145mm)
BLB 000
(100 x 165mm)
(110 x 160mm)
120 x 215mm
(150 x 215mm)
C (C5)
150 x 215mm
(140 x 195mm)
BLB 00
(150 x 215mm)
(150 x 210mm)
180 x 265mm
220 x 265mm
(220 x 340mm)
F (C4)
230 x 335mm
(220 x 320mm)
(220 x 340mm)
(220 x 330mm)
240 x 335mm
270 x 360mm
300 x 445mm
350 x 470mm