Bcmass up to orderαs4

We evaluate in perturbative QCD, up to order ${\alpha }_s^4,$ the mass of the $B_c.$ We use the so-called $1S$ mass in order to improve the convergence of the perturbative series. Our result is ${E(B}_c{)}_{\mathrm{}\mathrm{pert}}{=6326\mathrm{}}_{-9}^{+29\mathrm{}}$ MeV. Nonperturbative effects are discussed. A comparison with potential models seems to be consistent with nonperturbative contributions of the order $-(40\mathrm{}–100)$ MeV.