This paper presents a strength calculation for a statically determinate I-beam. Diagrams of internal force factors (transverse forces and bending moments) are constructed and the number of the I-beam is selected according to the given external load and the values of the material strength characteristics. The given material characteristics are permissible normal stress, elastic modulus and permissible shear stress. The strength of a beam with a selected cross-section for shear stresses was tested. To construct the I-beam elastic line, the deflections of cross-sections with a unit interval along the length are calculated. The beam deflections were calculated using the universal elastic line equation. The obtained value of the maximum beam deflection made it possible to draw a conclusion about the beam sufficient hardness and operability under given external loads.