NEB 5-alpha cells tested with pUC19
Estimate efficiency from a dilution series.
Transformation Efficiency Calculator
FigranTurn colony counts into cfu/µg from one plate or a whole dilution series.
- Several plates and dilutions
- Check against cell specs
- Compare transformations
Transformation efficiency
2.0 × 10⁹ cfu/µglog₁₀ 9.29 · 95% CI 1.7–2.3 × 10⁹
196 colonies on 1 plate · DNA on selected plates: 0.1 pg
| Dilution | µL | Colonies | Status |
|---|---|---|---|
| 1:10 | 100 | TNTC | TNTC |
| 1:100 | 100 | 196 | Used |
| 1:1,000 | 100 | 21 | Below 30 |
Transformants in the recovery: 1.96 × 10⁵
Within the selected cell spec · NEB 5-alpha (C2987H/I/P/U) (1.0 × 10⁹–3.0 × 10⁹ cfu/µg)
Next time: 100 µL · 1:100 should give 30–300 colonies.
Transformation efficiency calculator examples
Start with an example and adapt it to your experiment.
NEB worked example: one plate
Calculate efficiency from the C2925 FAQ.
Two-step dilution before plating
Account for a dilution made before plating.
Electroporation efficiency of NEB 10-beta cells
Compare an electroporation result with its cell spec.
Ligation with a vector-only control
Compare a ligation with its background control.
Homemade CaCl₂ DH5α cells
Compare three batches of homemade cells.
Library size from an electroporated ligation
Estimate the number of transformants in recovery.
pGLO teaching-lab transformation
The 510 µL total includes the DNA volume.
How to calculate transformation efficiency
Calculate and share your result in four steps.
1Enter DNA
Enter the DNA concentration and volume or its mass.
2Set recovery
Choose cells and enter the recovery volumes.
3Enter plates
Enter each dilution, plated volume and colony count.
4Take your result
Copy the result or export your data.
Transformation efficiency formula
The transformation efficiency equation divides colony counts by DNA plated.
For the NEB C2992 example: 150 ÷ (0.0001 × 30 ÷ 300 ÷ 100) = 1.5 × 10⁹ cfu/µg. Exact 95% confidence intervals use the Poisson count.
References: NEB C2992 FAQ
Competent cell efficiency by strain
Compare manufacturer specifications for selected strains.
| Cells | Chemically competent (cfu/µg) | Electrocompetent (cfu/µg) | Typical use |
|---|---|---|---|
| NEB 5-alphaC2987H/I/P/U | 1.0 × 10⁹– | — | Routine cloning |
| NEB 5-alphaC2987R | 1.0 × 10⁸– | — | Routine cloning |
| NEB 5-alpha F′IqC2992H/I | 1.0 × 10⁹– | — | Toxic gene cloning |
| NEB 10-betaC3019H/I | 1.0 × 10⁹– | — | Large plasmids |
| NEB 10-betaC3019P | 1.0 × 10⁸– | — | Large plasmids |
| NEB TurboC2984H/I | 1.0 × 10⁹– | — | Fast growth |
| NEB StableC3040H/I | 1.0 × 10⁹– | — | Unstable inserts |
| NEB StableC3040P | 1.0 × 10⁸– | — | Unstable inserts |
| NEB dam⁻/dcm⁻C2925H/I | 1.0 × 10⁶– | — | Unmethylated DNA |
| NEB 10-beta ElectrocompetentC3020K | — | > 2.0 × 10¹⁰ | Large plasmids |
| NEB Stable ElectrocompetentC3041K | — | > 1.0 × 10¹⁰ | Unstable inserts |
| NEB 5-alpha SubcloningC2988J | > 1.0 × 10⁶ | — | Routine cloning |
| Invitrogen TOP10C404010 | > 1.0 × 10⁹ | — | Routine cloning |
| Invitrogen MAX Efficiency DH5α T1R12297016 | > 1.0 × 10⁹ | — | Routine cloning |
| Invitrogen Subcloning Efficiency DH5α18265017 | > 1.0 × 10⁶ | — | Routine cloning |
| Agilent XL10-Gold200315 | ≥ 5.0 × 10⁹ | — | Large plasmids |
| Promega JM109 High EfficiencyL2001 | > 1.0 × 10⁸ | — | Routine cloning |
These specifications are measured using control plasmid under manufacturer conditions. Electrocompetent NEB 10-beta cells have a higher specified minimum than their chemically competent counterpart.
References: NEB Competent Cell Selection Guide · Invitrogen · Agilent · Promega
Transformation efficiency calculator FAQ
What is transformation efficiency?
It is the number of colony-forming units obtained per microgram of transformed DNA, usually measured with a small amount of control plasmid. It measures bacterial transformation performance for the selected cells and DNA.
What units is transformation efficiency reported in?
It is usually reported as cfu/µg. Multiply cfu/ng by 1,000 to convert to cfu/µg.
What is a good transformation efficiency for E. coli?
Compare the result with the specification for your cells and protocol; high-efficiency and subcloning cells have different specifications.
Why is my transformation efficiency low?
Cell handling, recovery, DNA quality and antibiotic selection can affect the count. A control plasmid helps distinguish cell performance from problems with the DNA.
How do I combine plates from several dilutions?
Add the countable colonies and divide by the total DNA on those plates. Recovery volume here is cells plus medium; enter replicates as separate plates.
Which plates should I count?
Use plates in your chosen countable range when available. TNTC plates are excluded, and low counts have wider confidence intervals.
How much DNA should I use to test competent cells?
Follow your cell manufacturer’s protocol; NEB recommends clean supercoiled pUC19 in the 100 pg–1 ng range.
How do I compare a ligation with a vector-only control?
Use Compare and mark the vector-only row as background. Compare cfu/µg when DNA amounts differ; a ligation calculator can help plan the preceding reaction.
Is transformation efficiency the same as CFU/mL?
No. CFU/mL describes viable cells per volume, while cfu/µg describes transformants per mass of DNA. Transformation frequency also requires a viable-cell count. CFU Calculator.
Check your next batch of competent cells
Turn your plate counts into a result for your lab record.
Calculate efficiency