This overall score is made up of: ease of loading/unloading (50%), ease of fitting to the roof bars (25%) and lock/lid opening (25%).

How easy the roof box is to fit to the car's roof bars. 

How easy it is to load and unload items into and out of the roof box. The best-scoring models are reasonably wide so they are easy to reach from the side of the car.

How easy it is to open and close the lid, and lock or unlock it. The best-scoring models can be opened from either side, so you can do it from the passenger side, which is safer if you've pulled over on the side of the road.

How much more fuel you're likely to use when carrying the roof box. 

We recommend car roof boxes that score at least 85% overall.

Recommended or typical retail price.

Based on the front area of the car roof box, used to assess fuel use.

The manufacturer's stated volume of the box, in litres.

The manufacturer's stated maximum load weight for the box, in kilograms.

Weight of the box itself. Keep in mind that when assessing the carrying capacity, you'll need to take the weight of the box off this capacity. For example, where a carrying capacity is 75kg and the weight of the box is 15kg, actual carrying capacity is 60kg.

This is the side from which you can unlock and lock the box. Ideally this is on the passenger side, so that when you stop by the side of the road to unlock, you aren't standing on the traffic side.

The manufacturer's recommended maximum speed in km/h with the box fitted (where stated).

The recommended distance in mm between the roof rack bars when mounting the box.

The number of straps inside the box for securing the contents.