byte[] original = new byte[30] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 };
int width = 5;
int height = original.Length / width;
byte[,] arr = new byte[width, height];
int x = 0;
int y = 0;
for (int i = 0; i < original.Length; ++i)
{
arr[x, y] = original[i];
x++;
if (x == width)
{
x = 0;
y++;
}
}