Cofactor Calculator (3x3)

This cofactor calculator finds the minor and the cofactor of any single entry in a 3 by 3 matrix, the two building blocks used to expand a determinant, build the adjugate and compute a matrix inverse. Enter the nine entries of your matrix into the m11 through m33 fields, then choose the row i and column j of the entry you want using the two dropdowns. The calculator deletes that row and column, takes the determinant of the remaining 2 by 2 matrix to find the minor, then multiplies it by the checkerboard sign of minus one to the power i plus j to give the cofactor. The results panel shows the cofactor as the headline figure, alongside the minor and the sign applied, so you see how the answer was built, not just the number itself. Change any entry or the chosen position and the result updates straight away, making it easy to check working by hand or step through every position in a matrix. Try the default identity matrix at row 1, column 1 for a simple worked case where the minor is 1, the sign is plus, and the cofactor is 1. It is a study and checking tool for algebra and linear algebra students, so enter accurate values and treat the output as a check on your own working, not a substitute for understanding the method.

Calculate.co.nz is proud to be partnered with Health Based Building, a leader in sustainable and health-conscious building innovation. With over a century of experience, they develop high-performance systems like Foreverbreathe Specification, Magnum Board, and Foreverbreathe Paints to support energy-efficient, non-toxic living environments. Their commitment to healthier homes aligns with our belief that informed choices lead to better outcomes for Kiwi households.