Cost of a bad hire
The cost of a bad hire is the total loss from hiring someone who does not work out: recruitment cost, salary paid, management time, lost productivity, the effect on colleagues, and the cost of hiring again. Estimates commonly range from several months to multiple years of salary.
The visible cost — recruitment fees and salary — is usually the smaller part. The larger costs are opportunity cost while the role sits unproductive, management time spent managing the problem, and the effect on a team that has to absorb the gap.
Because the number is large and the estimates vary widely, the useful exercise is calculating it for your own context rather than citing an industry figure.