All Microbiology Tools
Bacterial Growth Calculator
Model exponential bacterial growth. Calculate population size, generation number, and growth curves over time.
CFU Calculator
Calculate colony forming units per mL from plate counts. Accounts for dilution factor and plated volume.
OD600 Cell Density Calculator
Convert OD600 absorbance readings to cell density (cells/mL). Includes dilution correction and species presets.
Antibiotic Stock Solution Calculator
Calculate how to prepare antibiotic stock solutions and working concentrations for culture media.
Transformation Efficiency Calculator
Calculate bacterial transformation efficiency (CFU/µg DNA) from plate counts and plating parameters.
Plating Dilution Calculator
Determine the correct dilution factor and volume for plating to achieve countable colonies (30–300 CFU).
Doubling Time Calculator
Calculate bacterial doubling time and specific growth rate from two OD600 or cell count measurements.
Growth Rate Calculator
Calculate specific growth rate (µ), lag phase, and log phase parameters from multi-point growth data.
Antibiotic MIC Calculator
Calculate minimum inhibitory concentration from broth microdilution data. Determine MIC50 and MIC90.
Culture Media Calculator
Scale culture media recipes (LB, M9, BHI, SOC) to any volume. Auto-calculates each component amount.
Viable Cell Count Calculator
Calculate total and viable cell counts from hemocytometer data. Includes trypan blue exclusion method.
Contamination Guide
Identify and troubleshoot common lab contamination types. Visual guide with prevention and remediation steps.
Frequently Asked Questions
What is the difference between CFU/mL and cells/mL?
CFU/mL (colony forming units per milliliter) counts only viable, culturable bacteria that can grow into colonies on agar plates. Cells/mL counts all cells — including dead or non-culturable ones — and is typically measured by direct microscopy or OD600 conversion. For most lab purposes, CFU/mL is the gold standard for viable cell quantification, while OD600-based cell/mL estimates are faster but less precise. The two values can differ significantly when culture viability is low, for example after heat or antibiotic treatment.
How do I calculate bacterial doubling time from OD600 readings?
To calculate doubling time, take two OD600 readings during exponential (log) phase growth separated by a known time interval. The formula is: td = (t2 − t1) × ln(2) / ln(OD2/OD1), where t1 and t2 are the time points and OD1 and OD2 are the corresponding absorbance values. It is critical that both readings fall within the linear range of the spectrophotometer (typically OD600 0.1–0.8) and that the culture is in log phase, not lag or stationary phase. Our Doubling Time Calculator automates this computation.
What is a good transformation efficiency for E. coli?
Transformation efficiency is expressed as colony forming units per microgram of plasmid DNA (CFU/µg). Chemically competent E. coli cells typically yield 10⁶–10⁸ CFU/µg, while electrocompetent cells can reach 10⁹–10¹⁰ CFU/µg. For routine cloning, 10⁷ CFU/µg is considered acceptable. Lower efficiencies may indicate degraded DNA, improper heat shock timing, or cells that were not competent enough. Our Transformation Efficiency Calculator helps you determine your CFU/µg from plate counts automatically.
How do I prepare antibiotic stock solutions for bacterial culture?
Stock solutions are typically prepared at 1000× the working concentration to allow easy addition of small volumes to media. For example, ampicillin is commonly used at 100 µg/mL in culture, so a 100 mg/mL stock is prepared in sterile water, filter-sterilized through a 0.22 µm membrane, and stored in aliquots at −20°C. Most antibiotic stocks are stable for 6–12 months at −20°C. Our Antibiotic Stock Solution Calculator determines the exact mass to dissolve in a given solvent volume to reach your target stock concentration.
How many dilutions do I need to get countable colonies on a plate?
The countable range for standard agar plates is 30–300 colonies per plate (25–250 for some guidelines). If you do not know the approximate cell density of your sample, performing a serial dilution series spanning 10⁻¹ through 10⁻⁷ is recommended. For an overnight E. coli culture at approximately 10⁹ CFU/mL, a 10⁻⁶ dilution plated at 0.1 mL should yield roughly 100 colonies. Our Plating Dilution Calculator takes your estimated cell density and target colony count to recommend the correct dilution factor and plated volume.