Shipping Box Sizes: Pick the Right One Every Time

Author | Date: 11/1/2025

The Right Shipping Box Size Saves More Than Space

Ever received a parcel that’s five times bigger than the actual product — stuffed with air pillows and wasted cardboard? That’s not just annoying — it’s expensive, wasteful, and bad for your brand image.

Choosing the right shipping box size saves money on postage, protects your product, and improves the unboxing experience.

In this guide, we’ll show you how to measure boxes correctly, understand standard sizes, and even go custom when needed.

Understanding Shipping Box Sizes (and How They’re Measured)

The 3 Dimensions You Must Know

All shipping boxes are measured using Length × Width × Height, in that order. These measurements refer to the internal dimensions — the usable space inside the box.

Couriers calculate shipping cost using volumetric weight:

L × W × H ÷ divisor (often 5000 or 6000)

That means even lightweight items can cost more to ship if your box is oversized.

💡 Pro Tip

Always check whether your supplier lists internal or external measurements — corrugated walls can add 3–5mm per side.

How to Measure a Shipping Box Correctly?

Length: The longest side of the box opening.
Width: The shorter side of the opening.
Height: From the base to the top when closed.

Example: A 12 × 9 × 4 inch box means 12 inches long, 9 wide, and 4 high (internal space).
Leave at least 10–15 mm of room for padding or inserts.

💡 Visual Tip

Always measure from inside edge to inside edge — never include outer flaps.

Standard Shipping Box Sizes (Quick Reference Chart)

Size	Dimensions (inches)	Common Use
Small	6 × 4 × 3	Jewellery, small gadgets, cosmetics
Medium	9 × 6 × 4	Skincare, candles, accessories
Large	12 × 9 × 6	Apparel, shoes, retail boxes
Extra Large	16 × 12 × 10	Bulk goods, hampers, subscription kits

Metric Conversion (for International Readers)

Size	Inches	Centimetres
Small	6 × 4 × 3	15.2 × 10.2 × 7.6
Medium	9 × 6 × 4	22.9 × 15.2 × 10.2
Large	12 × 9 × 6	30.5 × 22.9 × 15.2
Extra Large	16 × 12 × 10	40.6 × 30.5 × 25.4

Always check your courier’s dimensional rules — some (like Royal Mail) measure in cm, others in inches.

Factors to Consider When Choosing Shipping Box Sizes

Product Type and Fragility

Fragile products like glassware or candles need extra cushioning — go slightly larger. Non-fragile items (like books or apparel) can fit more snugly.

Weight vs Volume

Couriers use dimensional weight, not just actual weight. That means a large, lightweight box can cost more than a compact heavy one.

Shipping Method & Courier Rules

Each courier has its own size tiers:

Royal Mail medium parcel: up to 61 × 46 × 46 cm
DHL / FedEx: dimensional weight calculators determine price

Always check maximum limits before dispatch.

Branding & Unboxing Experience

A box that fits perfectly doesn’t just save filler — it looks premium and intentional.

Good sizing = better protection, lower returns, and happier customers.

Different Box Sizes for Different Shipping Needs

Product Type	Recommended Box Size	Material Type
Candles & Skincare	9 × 6 × 3 (Medium)	Corrugated Cardboard
Apparel & Textiles	12 × 9 × 4 (Large)	Mailer or Rigid Box
Subscription Kits	Custom Size	Corrugated or Rigid
Electronics	10 × 8 × 4	Double-Wall Cardboard
Gift Hampers	16 × 12 × 6	Rigid or Thick Corrugated

Normal, Medium, and Large Shipping Box Sizes — What’s the Difference?

Small / Normal Box: around 9×6×3 inches — used for lightweight, compact items.
Medium Box: 12×9×4 inches — fits clothing, skincare, or small bundles.
Large Box: 16×12×6 inches or more — designed for bulk or multi-item orders.

Bigger isn’t always better — oversized boxes increase shipping costs and waste. Always measure your product + padding before bulk ordering.

Custom Size Shipping Boxes — When to Go Custom

Custom box sizing is ideal when:

You sell irregular-shaped products (candles, jars, bottles).
You want branded, snug-fit packaging for a luxury feel.
You’re tired of wasting filler material and shipping cost.

With Buy Packaging Boxes, you can order custom size cardboard boxes printed with your logo, brand colours, and eco-friendly finishes — in small or bulk quantities.

(Explore our Custom Cardboard Boxes range.)

Eco-Friendly Tip — The Right Size = Lower Carbon Footprint

Choosing the perfect fit isn’t just smart business — it’s sustainable. Smaller boxes use less material, occupy less storage space, and reduce carbon emissions during transport.

Our eco-friendly kraft shipping boxes are recyclable and perfect for sustainable eCommerce.

(View our Eco-Friendly Packaging Solutions here.)

Common Shipping Box Mistakes to Avoid

Guessing sizes instead of measuring properly.
Ignoring dimensional weight — and paying extra shipping fees.
Using single-wall cardboard for heavy goods.
Standardising one box size for all items.
Overfilling boxes (causes bulging or tearing).

Quick Guide — Shipping Box Sizes in CM

Size	Inches	Centimetres
Small	6 × 4 × 3	15.2 × 10.2 × 7.6
Medium	9 × 6 × 4	22.9 × 15.2 × 10.2
Large	12 × 9 × 6	30.5 × 22.9 × 15.2
Extra Large	16 × 12 × 10	40.6 × 30.5 × 25.4

Note

Couriers like Royal Mail, DPD, and UPS use their own dimension limits — always confirm before shipping.

Final Thoughts — The Perfect Box Size Saves More Than Space

Right-sizing your shipping boxes means fewer damages, lower postage costs, and happier customers. Whether you’re shipping jewellery or jumpers, the perfect box fit makes every delivery look professional.

At Buy Packaging Boxes, we offer custom size shipping boxes in all styles — from corrugated mailers to rigid gift boxes — printed, branded, and built for your exact dimensions.

🔗 Learn more: Custom Cardboard Shipping Boxes

Shipping Box Questions? Sorted.

How do I measure a shipping box correctly?

Always measure the inside of the box — from one inner edge to the opposite inner edge — for length, width, and height. These are the true internal dimensions that determine what fits and how shipping is calculated.

What are standard shipping box sizes?

Common box sizes include:

Small: 6 × 4 × 3 inches (15.2 × 10.2 × 7.6 cm)
Medium: 9 × 6 × 4 inches (22.9 × 15.2 × 10.2 cm)
Large: 12 × 9 × 6 inches (30.5 × 22.9 × 15.2 cm)
Extra Large: 16 × 12 × 10 inches (40.6 × 30.5 × 25.4 cm)

These are widely used across eCommerce, retail, and courier shipments in the UK.

What size is a UK post box?

The Royal Mail post box slot typically measures around 25 cm wide × 4 cm high, so only large letter boxes or small parcel envelopes fit through. For thicker items, you’ll need to send them via small parcel size at a post office.

What size boxes does Royal Mail sell?

Royal Mail sells packaging that matches its size categories:

Small Parcel: up to 45 × 35 × 16 cm
Medium Parcel: up to 61 × 46 × 46 cm
Large Parcel: must be sent via Parcelforce (over 61 × 46 × 46 cm)

They also offer prepaid mailing boxes in these formats — ideal for eCommerce sellers.

Can I order shipping boxes in custom sizes?

Absolutely. At Buy Packaging Boxes, we create custom-size cardboard boxes to fit your products perfectly — no excess space, no wasted filler, and full branding flexibility.

What’s the average size for shipping clothes?

For shirts, jumpers, or folded apparel, a 12 × 9 × 4 inch (30.5 × 22.9 × 10.2 cm) box is ideal. It provides enough room for wrapping or tissue paper without bulking up the parcel.

Are shipping box sizes the same worldwide?

Not quite. The UK and EU use centimetres, while the US uses inches. Carriers like Royal Mail, DPD, and UPS all have slightly different measurement standards, so always check before shipping internationally.