In controlled conditions the coverage for the top coat coach enamel is 10 square metres per litre.
Reality is somewhat different but at least we have a datum point. As far as spraying is concerned, 10 square metres coverage can be achieved. But if rollering or brushing then work on 7-8 square metres. The paint is naturally applied in a thicker layer no matter how frugal you are.
So, if you are painting a Short Wheel Base or 90″ Land Rover inside and out; start with 3 litres. If only going round the outside then 2 litres may be sufficient. We are all different and our personal methods dictate we may use more or less, but these amounts won’t be far off.
As for wheels… again using Land Rover 16″ wheels as an example, I would suggest they get at least 2 coats inside and out. Normally I carefully brush paint these to get a good coverage. Carefully done, you can do it with the tyres on. If spraying, the general thoughts are to cover with 2 – 3 coats to get good coverage into all the corners and hard to get to places. Quantity wise I allow 1 litre for a set of 5.