Both IELTS & TOEFL are used by universities to measure an international students English proficiency. Although, in the US, TOEFL is the more widely accepted score, but IELTS is also accepted by most universities. so it's really a preferable.
Dear Aswin, The TOEFL is more commonly accepted by American institutions, while the IELTS is more commonly accepted overseas, but many schools accept scores from either exam. ... Generally speaking, the majority of United States schools surveyed stated they preferred TOEFL scores over scores of other English-language tests.
All the best