This letter presents a novel method for the analysis of tilted fiber Bragg grating (TFBG) transmission spectra. The processing method is based on the transmission spectrum contour length, which is calculated in the wavelength range where cladding modes appear. The proposed algorithm is based on a modified analysis method that is used in spectrometric surveys of gas spectra in cases with unknown or fluctuating baselines. Experimental results obtained using the proposed method are compared with results from the most commonly used TFBG spectral analysis methods that utilize global monitoring of cladding modes.