The use of resonant frequency is presently one of the most used non-destructive testing (NDT) methods to predict the mechanical properties of sawn timber. In most cases, only the first vibration mode is used to estimate the static modulus of elasticity (MOES). The use of other vibration modes (overtones) can improve the predictive capacity of this NDT. In this study, the dynamic modulus of elasticity (MOEdyn) obtained from the fundamental flexural resonant frequency and overtones of 38 structural size samples (2000 × 100 × 70 mm3) of Pinus sylvestris were analysed. The study was complemented with 16 small size samples (1000 × 20 × 8.7 mm3) of the same species to know the shear effect in samples with a very high length-to-depth ratio. For the structural size samples, a 6% decrease in the MOEdyn was detected each time the vibration mode increased. Using the second or third vibration mode offered lower errors in the prediction of the MOES than the fundamental resonant frequency. The lowest MOES prediction errors were obtained combining various vibration modes through power regression. This regression turned out to be a simple alternative to avoid the shear effect in the calculation of the MOEdyn.