Urinary parameters such as voided volume and flow rate are crucial for diagnosing dysuria. Conventional uroflowmeters (UFMs) measure urinary flow based on weight changes or impeller rotation. However, these devices may present hygiene-related issues due to direct contact with urine, and the results may not accurately represent normal urination because of differences in posture and environment. To address these issues, we developed a scale-type UFM that utilizes weight loss during urination to measure flow. In a previous study, we reported that the accuracy of the scale-type UFM was comparable to that of three medical UFMs when measured in young males. In that study, participants urinated into an impeller-type UFM (Freeflow^®), and urine ejected from the Freeflow was collected in a weighted UFM (P-Flowdiary^®) cup placed over another weighted UFM (PicoFlow2^®). However, as measurements using these medical UFMs were performed simultaneously, Freeflow, which was the first to contact the urine, may have reduced the flow rate and retained some urine. Thus, the present study aimed to determine whether the urinary flow rate slowed by Freeflow is less than the measurement error in young males (21.9 ± 1.0 years) and older males (66.7 ± 1.2 years). In addition, we measured the voided volume (VV), maximum flow rate (Qmax), and average flow rate (Qave) using two UFMs (P-Flowdiary and PicoFlow2, without Freeflow) and compared the results with those using three UFMs (including Freeflow) from the previous study. We also compared VV and flow rate between young and older males. A comparison of the results between with and without Freeflow showed no significant differences in error rates for VV, Qmax and Qave. The error rate range for VV measured by an electronic balance versus that by the three UFMs was 1.2%-6.5%. A comparison of Qmax and Qave measured by the two medical UFMs with those measured by the scale-type UFM showed errors of 11.1%-13.2% and 21.4%-23.1%, respectively. These results indicate that the effects of Freeflow on VV, Qmax, and Qave are within the measurement errors. In other words, Freeflow does not affect the measurements of UFMs positioned downstream. The average VV, Qmax, and Qave were, respectively, 259.1 ± 190.8 mL, 27.0 ± 7.0 mL/s, and 15.0 ± 4.0 mL/s in young males; and 162.0 ± 72.7 mL, 18.1 ± 4.14 mL/s, and 9.5 ± 2.3 mL/s in older males. All the values were significantly higher in young males than in older males as determined by t-test.