Calculating the effect of antibiotics or antiseptics on bacterial growth

The effectiveness of the chosen antibiotic or antiseptic can be measured numerically by using the formula πr², where r is the radius of the zone of inhibition.

Method

1. For π 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 calculate the radius, (r), eg 10 / 2 = 5 mm
3. Use the equation: πr²

For example: 3.14 × 5² = 3.14 × 25 = 78.5 mm²