Abstract Line ratio of O IV 1407.3Å/1401.1Å is calculated using mostly our own atomic and collisional data. Energy levels and oscillator strengths needed for this calculation have been calculated using a Hartree–Fock relativistic (HFR) approach. The electron collision strengths introduced in the statistic equilibrium equations are fitted by polynomials for different energies. Comparison has also been made with available theoretical results. The provided line ratio has been obtained for a set of electron densities from 108cm−3 to 1013cm−3 and for a fixed temperature of 50,000K.