[Purpose] This study aimed to evaluate the impact of lung function and peripheral muscle function on the six-minute walking distance (6MWD) in systemic sclerosis (SS) patients and, thereby, to develop an explanatory model of functional exercise capacity for these individuals. [Methods] In a cross-sectional study, 31 SS patients underwent pulmonary function testing (including spirometry, diffusing capacity for carbon monoxide [DLCO], and respiratory muscle strength), isometric dynamometry with surface electromyography, and the 6MWD. [Results] There was a significant correlation between the 6MWD (% predicted, 6MWD%) and the following parameters: height (r = 0.427) and DLCO (r = 0.404). In contrast, no other independent variable showed a significant correlation with the 6MWD% (r ≤ 0.257). The final prediction model for 6MWD% (adjusted R² = 0.456, SE of bias=12%) was 6MWD% _Gibbons = −131.3 + 1.16 × height_cm + 0.33 × DLCO_{% predicted}. [Conclusion] In SS patients, body height and pulmonary diffusion are the main determinants of the 6MWD. Our results justify further investigation of the performance of SS patients during exercise, which may increase the understanding of the pathophysiological mechanisms involved in the disease. The impact of these findings in SS patients may be useful for evaluating the effects of rehabilitation programs.