Didymus the Writer on Measures was a Greek scholar who lived during the Roman Imperial period, likely between the 1st and 3rd centuries CE. He is known only for a single surviving work, a technical treatise titled On Measures. His precise identity and dates are uncertain, and he is distinguished from the more famous Alexandrian scholar Didymus Chalcenterus by his specific focus on metrology, the study of weights and measures.

As a grammarian and metrologist, his role was part of a tradition of specialized scholarship that sought to systematize knowledge. His work On Measures explains the systems of measurement found in older Greek texts, such as those of Homer. This type of treatise was important for accurately interpreting classical literature, as well as for legal and commercial understanding.

According to modern scholars, his significance lies in preserving this specialized technical knowledge. His work exemplifies the cataloging and explanatory efforts of Roman-era grammarians who worked to clarify details of Greek language and culture for contemporary audiences. While an obscure figure, he contributes to our understanding of the practical, systematizing branches of ancient scholarship.