When does a production function satisfy increasing returns to scale?

When the total output increases in a larger proportion than the proportionate increase in the factor input, it is called increasing returns to scale.

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 increasing returns to scale.