How many letters are there in the Welsh alphabet?

The Welsh alphabet is usually represented as 28 letters:

a, b, c, ch, d, dd, e, f, ff, g, ng, h, i, l, ll, m, n, o, p, ph, r, rh, s, t, th, u, w, y

The letter J can also be added as it is commonly used (as in the surname Jones).