The integration of methods to quantify the physical demands [e.g., Rating Perceived Exertion (RPE)] in small-sided games (SSGs) in younger soccer players, has been scarcely studied. In addition, few studies have been addressing the impact of balanced vs. unbalanced SSGs, in particular in youth players' RPE. This study aimed to investigate differences between balanced and unbalanced format games in young soccer players' RPE, controlling for different playing field sizes. The sample comprised 10 field players and 2 goalkeepers (Gk) being 13,55±0,51 years-old. The players performed 6 randomized different situations, following an identical methodology across the training days: (1) 4Vs.4+Gk (2) 4Vs.5+Gk, and (3) 4Vs.6+Gk. All situations were performed in 30x25m and 40x30m. The game situations lasted 5 minutes of practice and another 5 minutes of rest. After the execution of all game situations, participants were asked individually about their self-perceived effort, using the OMNI effort scale. In unbalanced format games when the difference in the number of players increases, RPE is lower. This tendency seems to be more evident in smaller compared to bigger playing field areas. The difference in RPE scores considering different dimensions of playing space seems not to be linear. Balanced soccer SSGs promote higher RPE than unbalanced soccer SSG. More studies on the topic are required considering different playing field areas as well as different players' backgrounds.