It’s often difficult to understand how large an area is without measuring. You can pace out the length and width of your area and multiply them to get an approximate idea. An average stride is 1 metre, so if your driveway is 4 strides by 6 then this would be 24 square metres this would be all you/I will need to give a rough costing for example.
If you are currently not near your home, a common car like a Volkswagen Golf Hatchback has a footprint of around 8.5 square metres. With this in mind, you may be able to get a rough idea of the area you need to cover by thinking how many cars would be able to park in the area your need to clean.