Dependencies for calculating the theoretical stress concentration factor at the weld toe in a cruciform joint under tensile and bending loads have been obtained. The connection with complete penetration of the weld root is considered. The studies of the stress-strain state were conducted using the finite element method while varying the geometric parameters of the connection, followed by processing the computational experiment and constructing a nonlinear regression model. An assessment of the obtained dependencies is given in comparison with the results of the computational experiment, as well as with known calculated dependencies. The advantage of the obtained dependencies is their compact form, suitable for engineering calculations, and the most complete consideration of the influencing geometric parameters.