Small sonic nozzles (throat diameter $0.28{~}4.48mm$) were tested in the gas flow standard system. This standard system is composed of two bell provers and 5 column piston provers, compressor, filters, and dehumidifier. The discharge coefficients of small some nozzles are obtained and correlated as a function of throat Reynolds numbers with $0.316\%$ uncertainty at a confidence level $95\%$. The tested high Reynolds number was the lower limit of ISO 9300 specifications. The data are useful as data base for revision of ISO 9300.