Vanadium has two stable isotopes, namely ⁵⁰V and ⁵¹V, with the abundances of 0.3% and 99.7%, respectively. Natural variations in the isotopic composition of vanadium can provide valuable insight into the origin of vanadium containing compounds and pathways of the element in the environment. The large difference in the abundances between vanadium isotopes makes high precision absolute ⁵¹V/⁵⁰V isotope ratio measurements a very challenging task. Remaining analytical challenges have been responsible for the fact that last attempt to re-determine the atomic weight of vanadium was made decades ago, in 1977. The traditional method for calibration of isotope ratio mass spectrometer and the determination of absolute isotope ratios is based on the use of synthetic isotope mixtures of the same element. However, isotopically enriched ⁵⁰V isotope is extremely expensive. In this case, a viable alternative can be the determination of absolute isotope ratios through online normalisation to a simultaneously measured isotope ratio of another element (an internal standard) with known isotopic composition. In this work, n(⁵¹V)/n(⁵⁰V) isotope ratios were determined by MC-ICP-MS employing online normalisation to isotopically certified Fe standard that was admixed to the solutions of vanadium. Data obtained show that calibration based on the online normalisation is suitable for the determination of n(⁵¹V)/n(⁵⁰V) isotope ratios with combined standard uncertainties better than 0.4%. Performance of the available models to correct for instrumental isotope fractionation, including the exponential, power and regression models, was evaluated and compared in terms of accuracy and precision. Full uncertainty budgets for the measurements will be presented, with recommendations on improving the measurement protocol for achieving improved uncertainty. The knowledge gained is essential for studies concerned with obtaining SI-traceable ⁵¹V/⁵⁰V isotope ratios and re-determining the atomic weight of vanadium which are ongoing in our laboratory.