Although it is considered that the half-value layer (HVL) of diagnostic X-rays is important for quality assurance (QA) and quality control (QC), the HVL is not constantly monitored because ionization-chamber dosimetry is time-consuming and complicated. To verify the applicability of GAFCHROMIC XR type R (GAF-R) film for HVL measurement instead of monitoring the ionization-chamber, a single-strip method for measuring the HVL has been evaluated. The calibration curves of absorbed dose and film density were generated using this single-strip method with eight strips of GAF-R film. The single-strip method precisely evaluated the increment of the film density. The exposure parameters of the X-ray generator (KXO-50G) were 120 kV, 200 mA and 0.28 s. Absorbed doses ranged from 0 to 12 cGy in increments of 2 cGy. The coefficient of determination of the straight-line approximation was evaluated. The HVL values measured using the GAF-R and ionization-chamber (Radcal-1015 6 cc) methods were compared. The coefficients of determination of the straight-line approximation for eight pieces of GAF-R film ranged from 0.9903 to 0.9961. The HVLs (effective energies) obtained from the GAF-R and ionization-chamber were 5.10 mm (42.18 keV) and 4.45 mm (39.70 keV), respectively. The differences in HVL and effective energy values obtained by the two methods were 14.6% and 6.2%, respectively. The calibration curves of the individual GAF-R strips were similar straight lines. This suggested that GAF-R could be used to measure the HVL from the film-density growth without the need for ionization-chamber measurements.