The number of letters in an alphabet depends on the language.
In English, the alphabet consists of 26 letters, which are:
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, Z.
In Greek, the alphabet has 24 letters, which are:
Alpha (Α, α), Beta (Β, β), Gamma (Γ, γ), Delta (Δ, δ), Epsilon (Ε, ε), Zeta (Ζ, ζ), Eta (Η, η), Theta (Θ, θ), Iota (Ι, ι), Kappa (Κ, κ), Lambda (Λ, λ), Mu (Μ, μ), Nu (Ν, ν), Xi (Ξ, ξ), Omicron (Ο, ο), Pi (Π, π), Rho (Ρ, ρ), Sigma (Σ, σ/ς), Tau (Τ, τ), Upsilon (Υ, υ), Phi (Φ, φ), Chi (Χ, χ), Psi (Ψ, ψ), Omega (Ω, ω).
Thus, the English alphabet has 26 letters, while the Greek alphabet has 24.