For application in a room-temperature microbolometer to detect terahertz waves, "narrow-width effects" on the temperature coefficient of resistance (TCR) and resistivity (ρ) for platinum (Pt) and titanium (Ti) nanowires are investigated. The TCR and ρ of a thermistor could be described by empirical formulas with average measured widths for higher precision. The effect of width on TCR in Pt is lower than that in Ti. The noise equivalent power of the microbolometer could be improved by a factor of 2.3 by replacing the Ti thermistor with a Pt thermistor of the same width (100nm). The results provide a detailed understanding of the narrow-width effect on TCR for Pt and Ti, which, to our knowledge, is lacking at present.