This paper presents a statistical procedure for expressing factors or margins of safety in terms of failure probabilities. The procedure involves identifying the basic variables in a structural or stress analysis and evaluating the statistical measurements of these variables in terms of mean, standard deviations and variances. An approximate rule of statistical algebra is then applied to obtain the relationship between margins of safety and failure probabilities. The present paper is restricted to variables that exhibit a normal probability distribution. A discussion is given on the advantages and limitations of the present statistical approach and an example is used to illustrate the calculation procedure.