To find the scale factor for dilating a square from a side length of 8 units to a side length of 20 units, you can use the formula for the scale factor:
\[ \text{Scale Factor} = \frac{\text{New Side Length}}{\text{Original Side Length}} \]
In this case, the new side length is 20 units and the original side length is 8 units. Plugging in the values:
\[ \text{Scale Factor} = \frac{20}{8} = 2.5 \]
Thus, the scale factor is 2.5.