How to find out productivity

Dear Team,

We need assistance on how to calculate agent incoming call productivity. As per our KPI have to check individual productivity performance.

Kindly provide us the formula for calculation for productivity. And currently we used the below formula but unable find out the correct number.

“Productivity
Workload hours of agent over staffing hours
(Total Talk Time + Voice Idle+ ACW/ Working hours)”

Need help. Thanks

Raj