The certification of a new standard reference material for small‐angle scattering [NIST Standard Reference Material (SRM) 3600: Absolute Intensity Calibration Standard for Small‐Angle X‐ray Scattering (SAXS)], based on glassy carbon, is presented. Creation of this SRM relies on the intrinsic primary calibration capabilities of the ultra‐small‐angle X‐ray scattering technique. This article describes how the intensity calibration has been achieved and validated in the certified Q range, Q = 0.008–0.25 Å−1, together with the purpose, use and availability of the SRM. The intensity calibration afforded by this robust and stable SRM should be applicable universally to all SAXS instruments that employ a transmission measurement geometry, working with a wide range of X‐ray energies or wavelengths. The validation of the SRM SAXS intensity calibration using small‐angle neutron scattering (SANS) is discussed, together with the prospects for including SANS in a future renewal certification.