GetLength takes an integer that specifies the dimension of the array that you’re querying and returns its length. Length property returns the total number of items in an array:
int[,,] a = new int[10,11,12];
Console.WriteLine(a.Length); // 1320
Console.WriteLine(a.GetLength(0)); // 10
Console.WriteLine(a.GetLength(1)); // 11
Console.WriteLine(a.GetLength(2)); // 12