Calculator
McFarland Turbidity to CFU/mL Calculator
Convert a McFarland standard reading into an approximate bacterial concentration.
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Formula & Clinical Notes
Formula
CFU/mL ≈ McFarland × 3 × 10⁸
Clinical Notes
A 1.0 McFarland standard corresponds to approximately 3 × 10⁸ CFU/mL for most bacteria (e.g., Escherichia coli). A 0.5 McFarland standard is commonly used for susceptibility testing and corresponds to roughly 1.5 × 10⁸ CFU/mL. The relationship is organism-dependent and an approximation.
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