This study investigated the field attenuation characteristics of hearing protection devices (HPDs), differences in estimating the protection provided by HPDs with different rating methods, and suggested potential solutions on proper use of attenuation ratings to estimate the protection provided by HPDs. The binaural octave-band personal attenuation values obtained from 1583 field users with 3985 fits on seven HPDs were used to compute the field-rating values as described in the International Organization for Standardization standard ISO 4869-2:2018, and the octave-band noise reduction (OB NR) values of each fit for 100 noises. The estimated protection for 100 noises was compared within different rating methods. The OB NR values varied with quality of fit, noise spectra, and HPD. The quality of fit was a crucial factor. Deviations in estimating the protection given by different rating methods varied with HPD and quality of fit. The misuse of subtracting the single number rating (SNR) from A-weighted noise level magnified these deviations. The multiple-number rating gave a more accurate estimation of protection provided by the earmuff compared to SNR. Improving the quality of fit and including C-weighted noise level can reduce the variability and deviation in protection estimation for different noises.