Transformation Efficiency Calculator
Evaluate the quality and competency of your bacterial competent cells (e.g. E. coli DH5α) by calculating Colony Forming Units (CFU) per microgram of plasmid DNA.
Cloning inputs
Specify DNA amount, suspension and plated volumes, and colony counts.
Transformation Efficiency
* Equal to 7,500,000 colonies per μg DNA.
Expert Tip
High-efficiency commercial competent cells yield efficiencies $> 1.0 \times 10^8$ CFU/μg. Lab-prepared cells usually range from $1.0 \times 10^6$ to $1.0 \times 10^7$ CFU/μg.
Methodology & Calculations
Efficiency Equation
Transformation efficiency represents colonies generated per microgram of added DNA, adjusting for dilution factors during plating:
Improving Transformation Rates
To achieve optimal efficiency:
- Avoid heating competent cells during handling; thaw exclusively on ice.
- Ensure heat shock is strictly timed (typically 42°C for exactly 30-45 seconds for E. coli).
- Allow cells to recover in SOC or LB broth for 45-60 minutes at 37°C prior to plating.
How to Calculate Bacterial Transformation Efficiency
Efficiency represents the number of colony-forming units (CFU) produced per microgram of plasmid DNA:
Note Transformed DNA Mass
Record plasmid DNA mass used, e.g. 100 pg (0.0001 µg).
Calculate Fraction of DNA Plated
Determine the ratio of the volume plated on agar to the total transformation recovery volume: DNA Plated (µg) = Total DNA (µg) × (Volume Plated / Total Volume).
Compute Efficiency (CFU/µg)
Divide the number of colonies by the mass of DNA plated: Efficiency = Colonies / DNA Plated (µg).