Constant returns to scale means when increase in total output is proportional to increase in the quantities of inputs i.e there is equal increase in output and input.

Here, IQ₁, IQ₂ and IQ₃ represent the total output of 1000 units, 2000 units and 3000 units respectively.

As we can see EE₁ = E₁E₂ = E₂E₃, so it is constant returns to scale.

Therefore, constant returns to scale operate when total output increases exactly in the same proportion as an increase in the quantity of factor inputs.