As part of an effort to extend fundamental single-photon measurements into the macroscopic regime, we explore how best to assign photon-number uncertainties to output waveforms of a superconducting transition edge sensor and how those assignments change over that extended dynamic range. Three methods are used. At the lowest photon numbers (up to 20 photons), the widths of histogram peaks of individual waveforms are used to determine the uncertainty. From 100 to 1000 photons, mean waveforms are used to create a photon-number scale. The photon-number uncertainty of the detector in this range is given by the excess of the total variance of the photon number obtained from individual waveforms on this scale beyond the shot noise due to the source. In the midrange (from 10 to 100 photons), including a range where the two other methods do not produce definitive results, we fit waveforms to several adjacent mean waveforms to estimate the photon-number uncertainty. A one-standard-deviation uncertainty in photon number of no more than +/- 1 is found for pulses of up to 100 photons.