Gaius Calpurnius Flaccus was a Roman senator of the second century. He was attested suffect consul with Lucius Trebius Germanus as his colleague on 15 December of an undetermined year between 122 and 127. Both Flaccus and Germanus are primarily known from inscriptions. Géza Alföldy has suggested that Flaccus might be the son of a Calpurnius Flaccus, to whom Pliny the Younger wrote a short and chatty letter. Alföldy identified the son with another Gaius Calpurnius Flaccus, known from an inscription, who was flamen provinciae Hispaniae about the time of Hadrian's visit to Tarraco.