In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon ( a -C:H) films. a -C:H films with a hydrogen content varying from 29 to 47 at . % have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures (≪120 ° C ) applying a wide range of bias voltage, V_b , (-300 V ≪V_b≪+100 V ) . With the application of high negative V_b , the a -C:H films undergo a dehydrogenation process accompanied by a sharp structural modification from polymer- to fullerenelike films. The trend in the H content derived from elastic recoil detection analysis (ERDA) is quantitatively reproduced from the intensity of the C–H bands and states in the IR and XANES spectra, respectively, as well as from the photoluminescence (PL) background drop in the Raman spectra. Using the H contents obtained by ERDA as reference data, semiquantitative expressions are inferred for the amount of bonded hydrogen as a function of the experimental spectroscopic parameters, i.e., the integrated area of the IR C–H stretching band at about 2900 cm ^-1 , the PL background in visible Raman spectra, and the XANES intensity of the σ^* -CH peak.