Besides Sonia Gandhi, 64, in the seventh place and Nooyi, 55, in the fourth place, two other Indians made it to the list, which is dominated by politicians, businesswomen and leaders in media and entertainment.
While ICICI Bank CEO Chanda Kochhar, 49, was placed 43rd, Biocon Founder Chair, Kiran Mazumdar-Shaw, 58, finished at 99.
In naming Merkel the world's most powerful woman, the US business magazine called her the 'undisputed' leader of the European Union and head of its only 'real global economy'.
Merkel, 57, who has topped the list of the world's 100 most powerful women in all but one of the years since she became chancellor in November 2005, beat US Secretary of State Hillary Clinton and, in third place, Dilma Rousseff, who became Brazil's first woman president this year.
After Rousseff was Nooyi, Facebook chief operating officer Sheryl Sandberg;
philanthropist Melinda Gates, Sonia Gandhi, US First Lady Michelle Obama, International Monetary Fund chief Christine Lagarde, and Kraft Foods CEO Irene Rosenfeld.
"Our list reflects the diverse and dynamic paths to power for women today, whether leading a nation or setting the agenda on critical issues of our time," said Moira Forbes, president & publisher of ForbesWoman.
The list was heavily tilted toward Americans, 65 of the 100 places.
Australia, China, India and Britain each had three Lady Gaga, at age 25, is the youngest powerful woman on the list. She was in 11th place and the highest ranked entertainer on the list.
The oldest lady on the list was another perennial, Britain's 85-year-old Queen Elizabeth, who was ranked 49th.
The eclectic list includes 20 CEO's, eight heads of state and 22 single ladies. The average age was 54.
Some of the best known women include Oprah Winfrey (14), Beyonce Knowles (18), Angelina Jolie (29), Ellen DeGeneres (55) and "Harry Potter" author J.K. Rowling (61).