Updated project metadata. Here we present quantitative proteomics data used in the evaluation of quantitative accuracy. A human cell line, MCF7 was split into 9 aliquotes that were spiked with a dilution series of 57 protein standards of known amounts spanning 5 orders of magnitude. The protein extracts were trypsinized, and the peptides were analysed by LC-MS using either a label-free or a label-based (TMT 6-plex and iTRAQ 8-plex) quantification approach. The iTRAQ- and TMT-labelled samples were co-analysed and separated by HiRIEF (high resolution isoelectric focusing) prior LC-MS.