It is a long run concept. It refers to change in output when all inputs are variable.
- Constant returns to scale (CRS) is a property of production function that holds when a proportional increase in all inputs results in an increase in output by the same proportion.
- Increasing returns to scale (IRS) holds when a proportional increase in all inputs results in an increase in output by more than the proportion.
- Decreasing returns to scale (DRS) holds when a proportional increase in all inputs results in an increase in output by less than the proportion.