AbstractThe SKA and its pathfinders will enable studies of H i emission at higher redshifts than ever before. In moving beyond the local Universe, this will require the use of cosmologically appropriate formulae that have traditionally been simplified to their low-redshift approximations. In this paper, we summarise some of the most important relations for tracing H i emission in the SKA era, and present an online calculator to assist in the planning and analysis of observations (http://hifi.icrar.org).