To say "I'm hungry" in Japanese, the most common phrase is お腹がすいた (onaka ga suita), which literally means "my stomach is empty." It is a standard and polite way to express hunger and can be used in most situations. A slightly more casual version is お腹すいた (onaka suita), which drops the particle が (ga) for simplicity. In very informal settings, you might hear 腹減った (hara hetta), which translates to "my belly is empty." This phrase is colloquial and often used by men or among close friends. Alternatively, a cuter or childlike way to say it is ペコペコ (peko peko), an onomatopoeic word that conveys the sound of a growling stomach, often said as お腹ペコペコ (onaka peko peko).