Roof box size
A guide, not advice. Check your kit maker's figures before you buy or pack.
The calculator needs JavaScript. The worked example, sum and figures below show exactly how it works, so you can do it yourself. A guide, not advice.
Short answer
Enter the internal box dimensions, vehicle roof-load limit, box and bars weight, and the kit weight you plan to carry. The calculator estimates volume and checks the remaining load allowance. Use the lowest limit from your vehicle, bars and box instructions.
Worked example
| You enter | Value |
|---|---|
| Roof box internal length | 1.6 m |
| Roof box internal width | 0.7 m |
| Roof box internal height | 0.35 m |
| Vehicle maximum roof load from its manual | 75 kg |
| Roof box and bars weight | 15 kg |
| Kit weight to load in the box | 45 kg |
Entered kit weight is within the remaining roof-load allowance.
| Result | Value |
|---|---|
| Approximate internal volume | 392 litres (cuboid estimate) |
| Load allowance after box and bars | 60.0 kg |
| Weight comparison | Entered kit weight is within the remaining roof-load allowance. |
Show the working
- Internal cuboid volume: 1.6 × 0.7 × 0.35 m = 392 L
- Remaining load: 75 − 15 = 60.0 kg
- Compare kit 45 kg with remaining 60.0 kg
How it works
- Cuboid volume = internal length × width × height
- Remaining roof load = vehicle roof-load limit − roof box and bars weight
- Compare kit weight with remaining roof load
The vehicle's roof-load limit includes the box, bars and contents. Check the car, roof bars and box instructions; use the lowest applicable limit and observe speed guidance.
Our figures (adjustable)
These are our planning allowances and, once checked, typical figures with their sources. They aren't facts about your kit: change any of them in the calculator.
This calculator has no built-in defaults: every figure comes from you or your kit's own label.
What to buy
Shopping links will appear here once our retailer partners are confirmed. We don't rank kit by testing it: see our spec-based kit guides.
FAQs
Does the vehicle roof-load limit include the box?
Check your vehicle manual and equipment instructions. The limit can include the roof box, bars and contents; use the lowest applicable limit.
Does the calculated volume show how much I can pack?
It is a cuboid estimate. Curves, openings and the shape of your kit affect usable space; check the maker's capacity and loading advice.
Guides that use it
Roof boxes for camping
Roof boxes for camping: fit and load one to the maker's instructions, check your vehicle handbook roof load limit and keep heavy kit inside.