Retained austenite in heat treated steels was measured through the magnetic saturation and, for comparison, through X-ray diffraction. It was shown that the reference, the saturation of the austenite-free material of equivalent composition, is crucial for obtaining useful RA contents. 3 models were used for assessing the effect of alloy elements on the saturation of steel. The models yielded different results, different also from those obtained through XRD. In any case, however, each model yields more reliable reults than using plain iron as a reference.