Upper Lower Bounds

.Length

This property returns the number of elements in the array.

.GetLength

This method returns the number of elements in a particular dimension of the multi-dimensional array

int[,,] myArray = new int[5,6,7];
Console.WriteLine(myArray.Length); // 201, 5x6x7
Console.WriteLine(myArray.GetLength(0)); // 5
Console.WriteLine(myArray.GetLength(1)); // 6
Console.WriteLine(myArray.GetLength(2)); // 7

For a 1-dimensional array: Length and GetLength(0) are exactly the same.

For multi-dimensional arrays: Length is the product of all the dimensions
Length = GetLength(0) x ... x GetLength(Rank - 1)