How many liters of paint will cover 500 meters square at 5mm thick?

A gallon of paint will cover about 300 square feetof wall area. So it will depend on the surface you are painting but in general square 5 gallons will cover approximately 1500square feet. Some manufacturers stretch ... If you can't decide between 4 or 5 gallons, go with 5 and buy it in a 5-gallon container. It should actually be cheaper than three 1-gallon cans, and you're guaranteed the colors will be the same.