The iso management system standard does not stipulate the number of internal auditors, but the internal audit clause in the standard requires to ensure the objectivity and impartiality of the audit, so it is impossible to form self-audit and mutual audit in actual audit. An enterprise must have at least three internal auditors to meet this requirement, and only consider that auditors need at least two internal auditors if they don't audit their own work.
How many internal auditors an enterprise needs to train is related to the size of the company, the complexity of its departments and products. Internal auditors are also human resources, so it is good to meet the needs. If conditions permit, the department with system-related work will train one or two internal auditors to supervise and guide the system-related work of the department, so that it is easier to promote the system work in various departments, and the implementation and supervision will be relatively in place. Those who have their own jobs and work as internal auditors should appropriately increase their remuneration.
If you want to train more internal auditors, you can invite certification bodies to train in the company, and the general cost will be lower than that of external training.