Introduction In physiotherapeutic diagnostic processes, various tools and methods may be used. However, price and availability may limit their daily use in clinical practice. Therefore, the suggestion that smartphones with specific applications may be useful as diagnostic tools can be found in the literature. However, before using them in clinical practice, it is important to verify their reliability. The aim of the study was to evaluate the consistency of measurements of the curvatures in the sagittal plane performed with the Saunders digital inclinometer and a smartphone application. Material and methods The study included 40 subjects aged 22-39 years (23.0 ± 3.7). All subjects had sagittal spinal curvatures (sacral slope - SS, lumbar lordosis - L, thoracic kyphosis - K, upper thoracic kyphosis - K1, lower thoracic kyphosis - K2) measured in both standing and sitting positions with the Saunders digital inclinometer and a smartphone application. Results In measurements performed with the use of the Saunders inclinometer and the smartphone, no significant differences were found between the size of the curvatures of the spine in a standing position (SS 19o ±8.2 vs. 17o ±8.4 p=0.3; L 32o ±11.1 vs. 29o ±10.3 p=0.2; K 43o ±8.4 vs. 41o ±8.1 p=0.2; K1 31o ±7.2 vs. 29.0 o ±7.3; K2 11o ±7.4 vs. 11.0 o ±6.7) and a sitting position (SS 3.75o ±8.9o p=0.8; L 5.8o ±9.06 vs. 5.2o ±8.5 p=0.75; K 40.0o ±8.1 vs. 36.7o ±7.9 p=0.6; K1 25.8o ±7.1 vs. 24.9 o ±7.1; K2 14.5o ±9.9 vs. 11.5 o ±9.4). Conclusions The examination of spinal curvatures in the sagittal plane using Saunders digital inclinometer and a smartphone application allows researchers to obtain reliable results. Therefore, smartphones can be used for an objective evaluation of the musculoskeletal system in daily clinical practice.