General strength:
* Je suis fort. (This is the most literal translation and is generally used for physical strength.)
* Je suis solide. (This means "I am solid" and can be used for physical or mental strength.)
Mental strength:
* Je suis courageux/courageuse. (This means "I am courageous" and emphasizes inner strength.)
* Je suis déterminé(e). (This means "I am determined" and emphasizes willpower.)
* Je suis résistant(e). (This means "I am resilient" and emphasizes the ability to overcome challenges.)
For a more poetic or metaphorical approach:
* J'ai du caractère. (This means "I have character" and emphasizes strength of personality.)
* Je suis une personne d'acier. (This means "I am a person of steel" and emphasizes unwavering strength.)
The best way to say "I am strong" depends on the context and the type of strength you want to express.