Abstract <p>This study investigates the performance of a newly designed high-porosity perforated-plate flow conditioner (HPPP) in improving flow measurement accuracy using orifice plates across a range of diameter ratios (β = 0.3–0.75). Experimental measurements were conducted to assess discharge coefficient deviations and axial velocity profiles downstream of the flow conditioners, with comparisons made against a standard Zanker conditioner and unconditioned flow. Results show that the HPPP conditioner consistently maintains discharge coefficient errors within the ±0.5% ISO 5167-2 tolerance for all tested β values, outperforming the Zanker design, particularly at low β where flow separation and sensitivity to disturbances are more pronounced. Velocity profile measurements further demonstrate the HPPP conditioner’s superior capability to restore flow symmetry and achieve a fully developed profile within a short downstream distance (<i>x</i>/<i>D</i> ≈ 9), as opposed to <i>x</i>/<i>D</i> ≈ 13.5 for the Zanker. These findings confirm the HPPP conditioner as an efficient solution for enhancing orifice flow metering accuracy across a broad range of flow conditions.</p>