© 2018 American Physical Society. Temperature sensing with nitrogen-vacancy (NV) centers using quantum techniques is very promising, and further development is expected. Recently, the optically detected magnetic-resonance (ODMR) spectrum of a high-density ensemble of NV centers was reproduced with noise parameters [inhomogeneous magnetic field, inhomogeneous strain (electric field) distribution, and homogeneous broadening] of the NV center ensemble. In this study, we use ODMR to estimate the noise parameters of the NV centers in several diamonds. These parameters strongly depend on the spin concentration. This knowledge is then applied to theoretically predict the temperature sensitivity. Using the diffraction-limited volume of 0.1μm3, which is the typical limit in confocal microscopy, we estimate the optimal sensitivity to be around 0.76mK/Hz with an NV center concentration of 5.0×1017/cm3. This sensitivity is much higher than previously reported sensitivities, demonstrating the excellent potential of temperature sensing with NV centers.