The effectiveness of the chosen antibiotic or antiseptic can be measured numerically by using the formula \( \pi {r}^{2}\). Using the diagram below.

1. For \( \pi\) use 3.14. This value may vary slightly in a specific question.
2. Measure the diameter of the zone of inhibition and divide it by 2 to find the radius.
3. Use the equation: \( \pi {r}^{2}\)

The radius of the clear zone is 5 mm (\( \text{radius} = \frac{diameter} {2}\))

The area of the clear zone = \( \pi {r}^{2}\)