The temperature of the cosmic microwave background (CMB) has been determined using data from the Far Infrared Absolute Spectrophotometer (FIRAS) and the Wilkinson Microwave Anisotropy Probe (WMAP). The FIRAS data, recalibrated using WMAP data, yields a CMB temperature of 2.7260 ± 0.0013 K. Measurements from the literature give a CMB temperature of 2.72548 ± 0.00057 K. The WMAP data, which measures intensity differences across the sky, is used to calibrate the velocity of the spacecraft relative to the CMB. This velocity is then used to form a differential spectrum of the CMB, which is fit to a single parameter—the CMB temperature. The WMAP velocity maps are corrected to the solar system's barycenter and used to generate temperature maps. These maps are convolved with the FIRAS beam to match its resolution. The FIRAS data is fit to a set of templates to account for various foregrounds. The CMB temperature is determined by fitting the differential spectrum to a model, with the temperature as the only adjustable parameter. The result is a temperature of 2.7260 ± 0.0013 K. The uncertainty in the temperature is dominated by FIRAS measurement noise, but correlations between frequencies and the PEP error term increase the uncertainty to 1.3 mK. The WMAP uncertainty is much smaller and does not significantly affect the final result. Combining FIRAS and WMAP uncertainties in quadrature gives a final uncertainty of 1.3 mK. The final CMB temperature estimate is 2.72548 ± 0.00057 K, which is consistent with other measurements. This value is derived from a combination of various methods and data, including FIRAS and WMAP data, and is considered the most accurate estimate of the CMB temperature.The temperature of the cosmic microwave background (CMB) has been determined using data from the Far Infrared Absolute Spectrophotometer (FIRAS) and the Wilkinson Microwave Anisotropy Probe (WMAP). The FIRAS data, recalibrated using WMAP data, yields a CMB temperature of 2.7260 ± 0.0013 K. Measurements from the literature give a CMB temperature of 2.72548 ± 0.00057 K. The WMAP data, which measures intensity differences across the sky, is used to calibrate the velocity of the spacecraft relative to the CMB. This velocity is then used to form a differential spectrum of the CMB, which is fit to a single parameter—the CMB temperature. The WMAP velocity maps are corrected to the solar system's barycenter and used to generate temperature maps. These maps are convolved with the FIRAS beam to match its resolution. The FIRAS data is fit to a set of templates to account for various foregrounds. The CMB temperature is determined by fitting the differential spectrum to a model, with the temperature as the only adjustable parameter. The result is a temperature of 2.7260 ± 0.0013 K. The uncertainty in the temperature is dominated by FIRAS measurement noise, but correlations between frequencies and the PEP error term increase the uncertainty to 1.3 mK. The WMAP uncertainty is much smaller and does not significantly affect the final result. Combining FIRAS and WMAP uncertainties in quadrature gives a final uncertainty of 1.3 mK. The final CMB temperature estimate is 2.72548 ± 0.00057 K, which is consistent with other measurements. This value is derived from a combination of various methods and data, including FIRAS and WMAP data, and is considered the most accurate estimate of the CMB temperature.