About 1500 N2O absolute wavenumbers measured in vacuum are provided. They cover a range of 225 cm−1, centered around 1250 cm−1. Their absolute accuracy extends from 50 to 125 × 10−6 cm−1 (1.5 to 4 MHz). The lines belong to 13 different absorption bands and to 4 different isotopic species, the rotational constants of which are given. Additional information on experimental intensity and halfwidth of the profiles can be used to appreciate the importance of each transition. These data, measured for the first time with a high information technique, are located in a spectral area where experimental wavenumber references were up to now practically absent. They should be useful for accurate calibration of diode laser and Fourier spectra.