Although foot diseases are common, only a few studies have detailed the biomechanical and anatomical components of each disorder. The most reliable diagnostic tool for flatfoot is X-ray radiography. Achieving a similar accurate and objective diagnosis using another assessment tool, such as plantar pressure measurements, can be more convenient in clinical practice. To identify foot plantar pressure characteristics that primarily detect flatfoot based on X-ray, which addresses the use of such assessments for flatfoot diagnosis. In addition, to compare between the normal foot, flatfoot with positive Foot Posture Index-6 (FPI), and flatfoot with positive FPI and radiographic measures. Sixty-two feet were examined from healthy female subjects aged 20.38 ± 1.10 years. According to the results of FPI and X-ray, each sample was assigned to one of the three groups (normal: negative FPI; FPI+: FPI ≥ +6; X-ray and FPI+: Arch Angle ≥ 165°, CP ≤ 12.3° and FPI ≥ +6) and compared using plantar pressure variables. As per normal group compared to X-ray and FPI+ group, there was a significant difference in the surface area (P-value: 0.01, 95 % CI: −26.58 to −3.62), force (P-value: 0.04, 95 % CI: −10.37 to −0.09), and pressure (P-value: 0.01, 95 % CI: −56.78 to −6.35) in the medial foot. Similarly, the arch index among the normal group and the X-ray and FPI+ group showed significant differences (Static AI; P-value: 0.003, 95 % CI: −0.21 to −0.04). There was a significant difference in plantar pressure between the normal feet and flatfeet with positive FPI and X-ray in the medial foot area. To attain a consensus among diagnostic approaches to identify flatfoot, the combined comparison of observational, foot pressure, and radiographic methods that have shown considerable reliability can be useful for clinical practice. •Plantar pressure measurements can be considered as a diagnostic tool for detection of flat foot.•Medial foot parameters are the most significant to differentiate flat foot.•Static arch index and medial foot surface have more sensitivity and specificity for detecting flat feet.