How do we know half-life of C14 is 5730 years?

In carbon dating methodology, we measure the presence of C14, and 5730 is given as a constant, the half-life of C14, in formula (0.693/T)N, and T is the half-life. But where do we get the constant from? Just who and how concluded that half-life of C14 is 5730 years?