John of Tynemouth was a 13th-century mathematician and geometer.
Little is known of his background, but he authored the Liber de curvis superficiebus Archimenidis, a tract about Archimedes' measurements of spheres. This is an important work in the history of medieval geometry, as it helped transmit Archimedes' ideas to other medieval scholars. The work itself follows closely Archimedes' own reasoning, but with enough differences to lead modern historians to believe the John's work was dependent on a Greek text from late antiquity.
The Liber survives in over 12 manuscripts, and was used by a number of other medieval scholars, including Robert Grosseteste, Jordanus de Nemore, Gerard of Brussels, and Roger Bacon.
Certain stylistic choices in the Liber suggest that John was also responsible for a number of other works, including a revision of another of Archimedes' works, the De Quadratura circuli, that is now in Florence at the Biblioteca Nazionale. Another such work that can possibly be assigned to John is two versions of the De Ysoperimetris, currently in Oxford University's Bodleian Library as manuscript (MS) Digby 174. Another possible editorial work by John is an edition of Euclid's Elements that was later cited by Roger of Bacon.