Gianna is the Italian short form of Giovanna — itself the feminine of Giovanni (John), from the Hebrew Yochanan, meaning "God is gracious." The name has been used in Italy for centuries.
Gianna entered the U.S. top 1000 in 1989 and has climbed dramatically. Today it sits in the U.S. top 50.
Gianna does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Gianna reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.