Sending parcels that slip straight through the letterbox has never been more important, especially with how often we shop and ship online these days. From knowing Royal Mail size limits to picking the right kind of box or envelope, a little planning goes a long way. Read till the end to discover everything you need to know about packaging for letter boxes in the UK.
Types of Royal Mail Sizes In The UK
Choosing the correct size category for your item helps ensure smooth delivery and accurate postage costs. Below are the main types of Royal Mail sizes currently used across the UK;
Medium Parcel
Medium Parcels are used for larger or heavier items like shoes, kitchenware, or electronics. The parcel must not exceed 61cm in length, 46cm in width and height, and can weigh up to 20kg.
Small Parcel
This category covers items that are a bit bulkier and don’t fit through a standard letterbox, such as small boxes, toys, or soft clothing. The maximum dimensions are 45cm x 35cm x 16cm, with a weight limit of 2kg.
Letter
This size is suitable for standard documents, greeting cards, or thin paper-based items. To qualify as a Letter, the item must not exceed 24cm in length, 16.5cm in width, and 0.5cm in thickness, with a maximum weight of 100g.
Large Letter
Large Letters are ideal for sending slim books, brochures, clothing accessories, or items in padded envelopes. The size must not go beyond 35.3cm x 25cm x 2.5cm and should weigh no more than 750g.
Why Does the Size of Letter Boxes Matter For Delivery?
The size of a letter box directly affects how smoothly and cost-effectively a parcel can be delivered. In the UK, many households rely on standard-sized letter boxes, which are designed to receive post without needing someone to answer the door.
If a parcel or mailer is designed to fit within these dimensions, it can be delivered safely and securely even when the recipient is not at home. This helps prevent missed deliveries, redelivery attempts, or parcels being left in unsafe places.
From a business perspective, using packaging that fits through a letter box means fewer delivery delays and a better experience for the customer. It also allows you to benefit from Royal Mail’s more affordable “Large Letter” or “Letter” postage rates, which can significantly reduce shipping costs.
How to Design Custom Mailer Boxes That Fit Through UK Letterboxes?
Custom packaging is now widely preferred by brands of all sizes. It not only protects the product but also strengthens brand identity and creates a better unboxing experience. In the UK, where many deliveries go through letterboxes, designing custom mailer boxes that meet Royal Mail’s size requirements is a cost-effective approach.
Let’s have a quick look on the process of designing custom mailer boxes;
- Check the maximum dimensions for letterbox delivery. For a large letter, Royal Mail allows maximum size of 35.3cm x 25cm x 2.5cm with 750g weight including box and the product.
- Before designing the box, measure the item carefully and keep some space for internal packaging to wrap the product inside for better protection.
- Pick lightweight and durable material such as corrugated cardboard or kraft paper. The material’s width should not exceed 2.5 cm and it should stand the wear during delivery.
- Design your box layout to be flat and rectangular and include foldable flaps and a secure closure system, such as a peel-and-seal strip or tuck-in lid, to keep the box shut without adding bulk.
- Use die-cut inserts or folded board to keep your item in place and avoid bulky padding like foam or thick bubble wrap.
- Print your brand logos or stickers on the package and keep it professional and minimal.
- Get a sample before ordering bulk of mailer boxes and post it to assess if it effectively serves the purpose. If successful, go for the bulk order.
- When packing, double-check the weight, seal the box neatly, and apply the correct postage label and delivery address and you are good to go.
Smart Tips for Choosing the Right Letterbox Packaging
Here are some simple tips you should consider for a better packaging experience in the UK;
- Select flat-folding or collapsible mailers if you ship different items regularly, allowing you to adjust and reduce storage space when not in use.
- Opt for packaging with moisture-resistant coating if you’re sending through UK weather conditions, which often include rain and damp.
- Choose packaging that includes a dedicated space for branding and addressing, helping you maintain a clean layout without overcrowding the design.
- Make sure your packaging complies with your courier’s machine-sorting requirements, which helps speed up delivery and reduces manual handling risks.
- For eco-conscious shipping, look for FSC-certified materials or suppliers offering carbon-neutral options that meet both environmental and functional needs.
- Always check the combined thickness of your product and packaging after sealing, as even slight overages may shift your item into a higher postage category.
How to Ensure Your Package Meets Royal Mail Guidelines?
If you are about to send something through Royal Mail, it is important to follow their packaging guidelines. Doing it right helps avoid delays, damage, or extra charges.
Here are some simple measures included in Royal Mail guidelines to help you post confidently and correctly:
Correct Labelling
Always write the full address clearly on the front, including postcode and country code for international deliveries. Use capital letters and black ink and make sure to include your return address as well.
Proper Sealing
Your package should be appropriately sealed and secured to avoid opening before arriving at the destination. All edges should be securely sealed.
Item Protection
For fragile items, it is good to use bubble wrap for added protection and to avoid damage during delivery. Such items should fit securely inside the packaging, as movements during delivery can cause damage.
Cushioning
You can add cushioning around your items in the form of bubble wraps or inserts to avoid breakage.
Add Required Information
Make sure to add barcodes, labels, and other necessary information required about the package and the item inside clearly.
Use Adhesive Tape Wisely
The tapes or other kinds of adhesive you are using should be according to the Royal Mail’s adhesive guidelines. Use it wisely and avoid covering your labels or other writings by placing tapes around them.
Small Parcel Care
If your package is classed as a Small Parcel, make sure it’s under the size limit and packed neatly. Pack the small parcels in such a way that the labels and instructions on the packaging surfaces are clearly visible.
Add Double Label
It is a good idea to place a second label with the delivery and return address inside the parcel. If the outer label gets damaged, this helps Royal Mail return it to you or deliver it correctly.
Common Mistakes to Avoid While Selecting a Letter Box
Choosing the proper packaging for letterbox delivery is crucial if you want to ensure safe, smooth, and cost-effective posting. Below are some common mistakes you should avoid while delivering a package to the letterbox;
Incorrect Material
Using thin or weak packaging can lead to damage during handling. It is best to choose sturdy, letterbox-friendly materials like padded envelopes or reinforced mailers.
Neglecting Guidelines
Royal Mail has precise size and weight limits for letterbox deliveries. Ignoring these can lead to extra charges or failed deliveries, so always check the latest size requirements.
Careless Sealing
Poorly sealed packaging can open in transit or be tampered with. Make sure all edges are closed adequately with strong tape or adhesive to keep your item secure.
Too Thick Packaging
If your parcel is too thick, it won’t fit through the letterbox and may be treated as a small parcel. Keep your packaging slim and within the 2.5cm limit for large letters.
Irregular Item Shape
Items with uneven shapes can get stuck or damaged in the letterbox. Try to pack your items in a flat, balanced way so they pass through easily and arrive safely.
The Bottom Line
Choosing the right packaging for letterbox delivery is all about ensuring efficiency, protecting your items, and presenting your brand or message with care. In the UK, where Royal Mail plays a central role in daily deliveries, using packaging that fits the required dimensions can streamline postage, reduce costs, and help avoid delivery issues. If you’re sending products regularly or building a small business, now is the time to reassess your packaging choices. Go for designs that are smart, functional, and compatible with standard letterboxes. Focus on materials that offer both durability and presentation, and always stay informed about current size standards. A well-thought packaging strategy reflects your attention to detail and helps build trust with the recipient.
Frequently Asked Questions
Does the weather affect letter box deliveries?
Yes, wet or windy weather can impact your letterbox deliveries. To be on the safer side, it is preferable to choose water-resistant materials in your packaging. Your items should dry and be secure from any moisture to prevent damage.
How can I track my mail or parcel?
You can easily track your item by using Royal Mail’s tracking services. When you post your parcel, you will get a tracking number on your receipt or shipping label. Simply enter this number on the Royal Mail website or app to see the latest updates.
Is delivering packages that fit through the letterbox cost-effective?
Packages that fit through a letterbox often fall under Royal Mail’s Letter size categories, which are much cheaper than Small Parcel rates. By keeping your packaging slim and within the size limits, you save on postage while still offering a convenient delivery experience.
Where to buy suitable packaging in Birmingham?
Birmingham offers plenty of options for buying packaging that works well with Royal Mail sizes. LSX Packaging and Ryman are some good options. You may consider Mailer Boxes for custom packaging or mailer boxes as well.
Can I reuse old packaging material to deliver items?
Yes, it is a great way to save money and reduce waste. Just make sure the packaging is clean, undamaged, and still sturdy enough to protect your item.
