An explicit mass formula for up and down quarks of three generations is proposed. Its structure contains an additional term in comparison to the efficient mass formula for charged leptons found out some time ago. The additional term is conjectured to be proportional to (3B + Q^(u,d))² = 25/9 or 4/9, where B = 1/3 and Q^(u,d) = 2/3 or -1/3 are the baryon number and electric charge of quarks. It is interesting to observe that the analogical term for charged leptons proportional to (L + Q^(e))², where L = 1 and Q^(e) = -1, would vanish consistently (here, F = 3B+L is the fermion number). Under this conjecture, the mass formula {ITALIC predicts} one quark mass, {ITALIC e.g.} m_b, in accordance with its experimental estimate, if the experimental estimations of five other quark masses are used as an input to determine five free parameters involved.

PACS numbers: 12.15.Ff, 12.15.Hh, 14.60.Pq