1 meter = approx 39.37 inches 1 square meter = 39.37"^2 multiply that by 20 to find area in square inches. Multiply that by 2" to find volume in cubic inches. 1 foof = 12 inches so 1 cubic ft = 12"^3 Divide that into previous answer to convert to cubic feet. 1 cubic yard = 3'^3 Divide that into previous answer to convert to cubic yards, which is the most common measurement of concrete. The ususal formula for concrete is 1 part cement + 2 parts sand + 3 parts gravel. Add those together and divide that into previous answer to find cement needed. Multiply that by 2 to find sand needed and by 3 to find gravel needed.You need 1/2 as much water as cement to mix.