Transformation Efficiency Calculator
Transformants per µg of plasmid DNA from your colony count, DNA amount, plated volume and dilution.
Transformation efficiency = colonies ÷ µg of DNA plated. 150 colonies from plating 100 µL of a 1,000 µL transformation that received 1 ng (0.001 µg) DNA: 150 ÷ (0.001 × 0.1) = 1.5 × 10⁶ cfu/µg.
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How to use it
- Enter the colonies counted on the plate.
- Enter the DNA added to the cells and its unit.
- Enter the total volume after recovery, the volume plated and any dilution.
What you enter
- Colonies
- DNA added
- Total recovery volume
- Volume plated
- Dilution
What you get
- Transformation efficiency (cfu/µg)
- DNA plated
- Competence grade
Formula
TE (cfu/µg) = colonies / [DNA (µg) × (V plated / V total) / dilution]
Worked example
Input: 150 colonies, 1 ng DNA, 100 µL of 1,000 µL plated
Result: 1.5 × 10⁶ cfu/µg
Typical of chemically competent cells; adequate for retransforming a plasmid.
Questions
How do you calculate transformation efficiency?
Work out how much DNA was on the plate (DNA added × volume plated ÷ total volume, ÷ any dilution) in µg, then divide the colony count by it.
What is a good transformation efficiency?
Home-made chemically competent E. coli usually reach 10⁶–10⁷ cfu/µg; commercial cloning cells 10⁸–10⁹; electrocompetent cells 10⁹–10¹⁰.
Why use pUC19 to measure efficiency?
A small supercoiled control plasmid transforms reliably, so it measures the cells rather than your ligation.
Why are there no colonies?
Check the antibiotic matches the plasmid, the heat shock (42 °C, 30–45 s), recovery time, and that the cells were never warmed or refrozen.
Limitations
- Only valid for counts in roughly the 30–300 colony range.
- Ligation reactions give lower efficiency than supercoiled plasmid.
References
- Green MR, Sambrook J (2012) Molecular Cloning: A Laboratory Manual, 4th ed. Cold Spring Harbor Laboratory Press.
Related reading
- How to Calculate Transformation Efficiency
- How to Calculate Transformation Efficiency: Formula, Examples, and Common Pitfalls
- Bacterial Transformation Troubleshooting: Low Efficiency and No Colonies
- E. coli Transformation: Mechanisms, Methods, and Best Practices
- Chemically Competent Cells: Mechanisms and Preparation Protocols
- Making Competent Cells: Mechanisms, Methods, and Troubleshooting
More Molecular Biology
- Codon Table (Interactive Genetic Code)
- Amino Acid Chart
- qPCR Efficiency & Standard Curve Calculator (Copy Number)
- ΔΔCt Calculator: qPCR Fold Change and Relative Expression
- Ligation Insert-to-Vector Mass Calculator
All free tools · By Dr. Zubair Khalid, DVM, MS, PhD.