Quantitative analysis by powder X-ray diffraction has long been carried out using calibration curves, a technique that requires preparing samples whose components are quantified, using pure or standard substances to obtain calibration curves. In recent years, quantitative analysis without calibration curves has become possible by calculating quantitative values from crystal structures. However, these methods require the crystal structures of the materials, limiting the applicable substances. With the Direct Derivation method introduced here, the quantitative weight fractions of individual crystalline phases can be derived from sets of integrated intensities collected in a wide 2q range, together with chemical composition data.