After seeing a 2020 Bridge Theatre performance, Nick Curtis of "Evening Standard" argued, "If the background logistics are sketchy – who made the human copies, and why? – the relationships between Salter and his offspring, and their differing reactions to finding that they are not unique, are right on the money. [...] It’s almost exactly an hour long and the ending is abrupt, but Churchill packs more ideas and feeling into that time than most dramatists manage at twice the length." Clive Davis of "The Times", however, panned the play as "both too short and too long" after seeing the same performance. Matt Wolf lauded "A Number" as a "beautiful play", and wrote that it "works not least as a thriller or bit of forensic detection, as Churchill plants clues prompting a reevaluation of the narrative at every turn." Arjun Neil Alim of "The Independent" stated that "Churchill, a political playwright par excellence, tactfully references current events. [...] Are 'Who are you?' and 'What are you made from?' the same question? Churchill’s answer comes in the form of a character who defines himself by his deeds and his loved ones, rather than the circumstances of his birth." Andrzej Lukowski of "Time Out" called the play a "masterpiece".