For infill panels, the expected strength is very close to the cracking strength; however, experimental values of the cracking strength are very scattered, and there is no formula to estimate it accurately. That is why some new codes have been assumed to focus on determining the expected strengths of Infill panels by their maximum strengths. In this paper, an extensive statistical analysis is conducted on experimental data to achieve a formula for the maximum (mostly referred as ultimate) strength of solid masonry infilled frames. For the ultimate strength, reliability of the existing empirical relations (9 formulas) is investigated, based on the available experimental data, categorized in accordance with their conning frames. The obtained results of 51 experimental specimens show that the formula, recommended by Maintone et al., is the best one; however, it mostly underestimates the ultimate strength and is more accurate for the inlls in concrete frames. The formula is also improved to have a better correlation with the experimental data.