The armor layer on the sea side of a rubble structure must be designed to protect against incident waves during storms. Formulas for armor stability and damage progression have been developed and are widely used for practical applications. However, none of the formulas accounts for the water depth at the toe of the structure explicitly. An alternative approach based on the maximum wave momentum flux at the toe of the structure is proposed in this article. Equations for sizing stable armor stone for constant incident waves and water level are proposed and calibrated using available data. Equations are also developed for determining damage progression in a life-cycle analysis involving varying wave and water level characteristics. The developed equations are calibrated using the damage progression tests conducted previously by the authors and verified using an additional 10 tests conducted for this article.