The Hirai 平井 medical house (sinicized Píngjǐng, fl. eighteenth century, mid-to-late Edo Japan) was a Japanese physician-family that specialised in the Hàn-to-Japanese measure conversion problem for the Zhāng Zhòngjǐng classical formulas. The principal extant work attributed to the family is the Kohō bunryōkō 古方分量考 (KR3ed102) — printed in 1793 (Kansei 5) by the collator 貞庵山人 (Tei’an Sanjin) under the family designation Hirai-shi 平井氏. The work is referenced in the preface alongside Hirai’s Yī héng 醫衡 — a companion treatise on Hàn-Japanese-measure calibration which the preface cites for the clinical-practical rule that the three high-toxicity Wūtóu formulas must not be re-administered.
The personal name Tíngshí (“Garden-stone”) is one variant transmission; the catalog records the family as 平井氏 without disambiguation, and no individual physician of the Hirai house is securely identified. The family probably operated in the Kohō-ha 古方派 (ancient-formulas) tradition of Yoshimasu Tōdō but specialised in the technical sub-discipline of dose-calibration rather than in clinical practice. Sparse biographical information.