June 18, 2025 Dean Horton

Roof Box Size Guide – What Capacity Do You Actually Need?

Choosing a roof box can be tricky — too small and you’ll still run out of space, too big and you might overdo the roof weight or run into fitting issues. This guide helps you pick the perfect roof box size based on real-world needs, from weekend getaways to family holidays.

📦 1. What Are the Standard Roof Box Sizes?

Most roof boxes fall into 3 size categories:

Box Size	Capacity (litres)	Fits...
Small	300–400L	Weekend gear, couple’s luggage
Medium	400–500L	Family of 3–4 for a few days
Large	500–650L	Camping kit, multiple cases, bulky items

🔗 Shop All Roof Boxes

👨👩👧👦 2. Match the Size to Your Travel Style

Ask yourself:

How many people are travelling?
Are you carrying soft bags, hard cases, or camping gear?
Do you need space for extras like folding chairs or prams?

Typical scenarios:

💼 Solo or couple weekends: 320–400L
👨👩👧 Small families: 450–500L
🏕️ Camping trips or bulky loads: 550L+

🔗 Read: Best Roof Box Accessories for Long Trips

📏 3. Measure Your Car & Roof Bars

Important: Your box must fit within the usable width of your roof bars.
Check:

Bar length (often 118cm–135cm)
Distance between bars (to line up with box mounting slots)
Boot clearance (longer boxes may restrict boot opening)

✅ Tip: For hatchbacks or smaller cars, choose a shorter, wider box instead of a long narrow one.

⚖️ 4. Know Your Weight Limits

Every vehicle has a maximum roof load, usually 50–100kg.

Total load =

Roof bars + roof box + contents

Example:

Roof bars: 6kg
Roof box: 15kg
Contents: 25kg
➡️ Total = 46kg — within most limits

🔗 Read: How to Fit a Roof Box Safely

🚙 5. Will You Be Using Other Roof Gear?

If you also plan to carry:

🚲 Bikes
🏕️ Roof tents
🛶 Kayaks or boards

Then choose a narrower roof box (60–70cm width) to leave room on the bars.

🔗 Read: Can You Fit a Bike Rack and Roof Box Together?

🧳 6. Final Tips for Picking the Right Roof Box

✅ Go bigger if you pack bulky or awkward items
✅ Prioritise aerodynamic shapes if doing long motorway trips
✅ Choose dual-side opening if you’ll be unloading from both sides
✅ Don’t forget to check garage or parking clearance!