With COVID-19 N95 respirator shortages, frontline medical personnel are forced to reuse this disposable - but sophisticated - multilayer textile respirator. Widely used for decontamination of nonporous surfaces, UV-C light has germicidal efficacy on porous, non-planar N95 respirators when ≥1.0 J/cm^2 dose is applied across all surfaces. Here, we address outstanding limitations of photochromic indicators (qualitative readout and insufficient dynamic range) and introduce a photochromic UV-C dose quantification technique for: (1) design of UV-C treatments and (2) in-process UV-C dose validation. Our methodology establishes that color-changing dosimetry can achieve the necessary accuracy (>90%), uncertainty (<10%), and UV-C specificity (>95%). Furthermore, we adapt consumer electronics for accessible quantitative readout and extend the dynamic range >10× using optical attenuators. In a measurement infeasible with radiometers, we observe striking 20× dose variation over 3D N95 facepieces. By transforming photochromic indicators into quantitative dosimeters, we illuminate critical design considerations for both photochromic indicators and UV-C decontamination.