The chart week runs from Friday to midnight Thursday, The Top 40 chart is first issued on Friday afternoons by BBC Radio 1 as The Official Chart from to , before the full Official Singles Chart Top 100 is posted on the Official Charts Company's website.
A rival chart show, The Vodafone Big Top 40, is based on downloads and commercial radio airplay and is broadcast Sunday afternoons from to across 140 local commercial radio stations around the United Kingdom.
For example, the BBC compiled its own chart based on an average of the music papers of the time; many songs announced as having reached number one on BBC Radio and Top of the Pops prior to 1969 are not listed as chart-toppers according to the legacy criteria of the Charts Company.
Before the compilation of sales of records, the music market measured a song's popularity by sales of sheet music.
The UK Singles Chart (currently entitled Official Singles Chart) is compiled by the Official Charts Company (OCC), on behalf of the British record industry, listing the top-selling singles in the United Kingdom, based upon physical sales, paid-for downloads and streaming.
To be eligible for the chart, a single is currently defined by the Official Charts Company (OCC) as either a 'single bundle' having no more than four tracks and not lasting longer than 25 minutes or one digital audio track not longer than 15 minutes with a minimum sale price of 40 pence. Some media outlets only list the Top 40 (such as the BBC) or the Top 75 (such as Music Week magazine) of this list.
The precise number of chart-toppers is debatable due to the profusion of competing charts from the 1950s to the 1980s, but the usual list used is that endorsed by the Guinness Book of British Hit Singles and subsequently adopted by the Official Charts Company.
The company regards a selected period of the New Musical Express chart (only from 1952 to 1960) and the Record Retailer chart from 1960 to 1969 as predecessors for the period prior to 11 February 1969, where multiples of competing charts (none official) coexisted side by side.
Around 6,500 British retail outlets contribute sales data, as well as most UK online digital-download stores.
Unlike charts in the United States, no airplay statistics are used for the official UK Singles Chart.