Minimum Inhibitory Concentration (MIC) Calculator
Use this tool to calculate antimicrobial concentration across a serial dilution panel and identify the MIC well concentration quickly.
What this MIC calculator does
The minimum inhibitory concentration (MIC) is the lowest antimicrobial concentration that prevents visible growth of a microorganism after incubation. In practical bench work, you usually generate a dilution series and then identify the well where growth stops. This calculator translates your dilution setup into exact concentrations and highlights the MIC concentration based on your selected well.
How to use the calculator
1) Enter your dilution setup
Set the concentration for Well 1 (your highest concentration), the dilution factor, and total number of wells tested.
2) Enter the MIC well
Select the well corresponding to the lowest concentration with no visible growth. The tool returns the estimated MIC in µg/mL and shows the full concentration table.
3) If growth appears everywhere
Check the “No inhibition observed” option. The calculator will report your MIC as greater than the lowest concentration tested (for example, MIC > 0.125 µg/mL).
Worked example
Suppose you start at 64 µg/mL in Well 1, run a two-fold dilution (factor 2), and test 10 wells. If the MIC well is 5, the concentration in that well is:
- Well 1: 64
- Well 2: 32
- Well 3: 16
- Well 4: 8
- Well 5: 4 µg/mL ← MIC
The estimated MIC is therefore 4 µg/mL.
Interpreting MIC results
An MIC value alone is not a clinical category. Susceptible/intermediate/resistant calls should be made using accepted breakpoint standards (for example, CLSI or EUCAST), correct organism identification, and validated lab methods.
- Lower MIC generally indicates greater in vitro potency against that isolate.
- Comparisons across drugs require caution because breakpoints differ by agent and organism.
- Replicate testing and quality controls are essential for reliability.
Common mistakes to avoid
Using the wrong well direction
Always keep your counting direction consistent with your dilution order. This calculator assumes Well 1 is highest concentration.
Confusing MBC with MIC
MIC reflects inhibition of visible growth, while minimum bactericidal concentration (MBC) reflects killing based on subculture. They are related but not equivalent.
Ignoring skipped wells
If your plate pattern is irregular (for example, trailing, skipped wells, contamination), treat the result as tentative and confirm with repeat testing.
Why this tool is useful
Even simple dilution panels can become error-prone when done manually under time pressure. A quick MIC calculator improves consistency, speeds reporting, and helps with record-keeping for research notes, student training, and method development.