English alphabet - Letter numbers and frequencies

The graphic below shows the frequency of letter usage in a particular sample of written English,[vague] although the frequencies vary somewhat according to the type of text.

Reference 1: Frequency.

Reference 2: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y and Z.

Source: http://en.wikipedia.org/wiki/English_alphabet