The Complete Guide to Choosing the Right Postal Box Size for Your Business

Why size selection matters

The right box size protects your product, minimises shipping costs, reduces void fill usage, and creates a professional presentation. Too large wastes money on materials and shipping; too small risks damage and looks unprofessional.

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Right-sized boxes reduce dimensional weight charges and carrier surcharges

Less void fill needed when the box fits the product properly

Oversized boxes increase damage risk because products shift during transit

Quick answer

Measure your product, add 3-5cm per side for cushioning, and check the total against carrier size bands. Most businesses need 3-5 box sizes to cover their product range. Aim for each box to fit within the cheapest applicable Royal Mail or courier pricing band. Order samples of candidate sizes and test-pack your products before committing to bulk orders.

How to measure

Measuring steps0 / 5 checked

Measure product length, width, and height at the widest points

Add 3-5cm to each dimension for cushioning material

Account for any irregular shapes or protrusions

Consider whether multiple products will ship in one box

Check the resulting dimensions against carrier pricing bands

Building your size range

Analyse your top-selling products and group them into size clusters.

Boxes with pre-scored height adjustments let you use one box for products of varying height.

Too many sizes creates inventory complexity. Aim for the minimum range that covers 90% of orders.

Shipping savings: optimising for carrier pricing or Royal Mail guidelines.

Royal Mail size bands

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Small parcel: up to 61cm x 46cm x 46cm, up to 2kg - cheapest parcel rate

Medium parcel: up to 61cm x 46cm x 46cm, up to 20kg - more expensive

Large letter: up to 35.3cm x 25cm x 2.5cm, up to 750g - cheapest for flat items

From ProcuraPack

Postal boxes in every size

Stock and custom sizes designed to fit Royal Mail and courier pricing bands.

Browse postal boxes

Frequently asked questions

Measure your product, add 3-5cm for cushioning, check against carrier pricing bands, and test-pack before ordering bulk.

Most businesses need 3-5 sizes to cover 90% of their product range.

3-5cm on each side between the product and box wall.

Yes, score lines let you reduce box height for shorter products, saving on shipping and materials.

Small parcel (up to 61cm x 46cm x 46cm, 2kg) is the most cost-effective parcel band.