# What is transformation efficiency?

Finds the transformation efficiency of competent cells, in colony-forming units per microgram of DNA, from the colonies counted, the DNA transformed and the share of the transformation that was plated, or the colonies to expect from a known efficiency.

- Page: https://www.acalculator.org/biology/transformation-efficiency-calculator
- JSON spec: https://www.acalculator.org/biology/transformation-efficiency-calculator.json
- Version: 014149a9e5a3

## Default answer

Example with the default inputs (Find Efficiency, Colonies counted 20, DNA transformed 100, DNA unit pg, Share plated from Volumes, Total volume after recovery (µL) 1,000, Extra dilution before plating (1 in …) 1, Volume plated (µL) 100): TE = 2 × 10⁶ cfu/µg.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| find | Find | The efficiency from a colony count, or the colonies to expect from an efficiency. |
| c | Colonies counted | The colonies on the plate you counted. |
| te | Efficiency (cfu/µg) | The transformation efficiency of the cells, such as 1e8 colony-forming units per µg. |
| dna | DNA transformed | The amount of plasmid DNA added to the competent cells. |
| u | DNA unit | Picograms, nanograms or micrograms of DNA. |
| how | Share plated from | Work out the share of the DNA that was plated from the volumes, or type it. |
| vt | Total volume after recovery (µL) | Competent cells plus the recovery medium (SOC), such as 50 + 950 = 1,000 µL. |
| x | Extra dilution before plating (1 in …) | A further dilution of the recovered cells before plating: 100 for 10 µL taken up to 1 mL; 1 for none. |
| vp | Volume plated (µL) | The volume spread on the plate you counted. |
| f | Fraction of the DNA plated | The share of the transformation that went on the plate, such as 0.1; the product of each dilution step. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| result | Answer | The efficiency in cfu per µg of DNA, or the colonies to expect. |
| efficiency | Transformation efficiency (cfu/µg) | Colonies ÷ µg of DNA ÷ the fraction plated. |
| expected | Expected colonies | The efficiency × µg of DNA × the fraction plated. |
| dnaUg | DNA transformed (µg) | The DNA added to the cells, in micrograms. |
| share | Fraction plated | The share of the transformation on the plate: volume plated ÷ (total volume × dilution). |
| onPlate | DNA on the plate (µg) | The micrograms of DNA that went on the plate: µg transformed × the fraction plated. |

## Method

TE = colonies ÷ (µg of DNA transformed × fraction plated); fraction plated = volume plated ÷ (total volume after recovery × extra dilution); expected colonies = TE × µg × fraction plated.

## Assumptions

- Every colony on the counted plate grew from one transformed cell, and the plate is countable (not a lawn).
- The total volume is the cells plus the recovery medium; the few µL of DNA added are left out, as in NEB’s examples.

## Worked examples

1. find = te, c = 20, dna = 100, u = pg, how = vol, vt = 1,000, vp = 100 gives efficiency = 2,000,000, share = 0.1, onPlate = 0.00001, result = TE = 2 × 10⁶ cfu/µg. Source: NEB, FAQ: How should I calculate the transformation efficiency (C2925)? (TE = Colonies/µg/Dilution; 20 colonies from 100 pg, 100 µl of 1,000 µl plated: 2 × 10⁶ cfu/µg), https://www.neb.com/en-us/faqs/how-should-i-calculate-the-transformation-efficiency-c2925.
2. find = te, c = 150, dna = 100, u = pg, how = vol, vt = 300, x = 100, vp = 30 gives efficiency = 1,500,000,000, share = 0.001, result = TE = 1.5 × 10⁹ cfu/µg. Source: NEB, FAQ: How should I calculate the transformation efficiency (C3040)? (150 colonies from 100 pg; dilution 10/300 × 30/1000 = 0.001: 1.5 × 10⁹ cfu/µg), https://www.neb.com/en-us/faqs/how-should-i-calculate-the-transformation-efficiency.
3. find = te, c = 50, dna = 1, u = ng, how = frac, f = 0.05 gives efficiency = 1,000,000, onPlate = 0.00005. Source: NEB, FAQ: How should I calculate the transformation efficiency (C2925)? (TE = Colonies/µg/Dilution; 20 colonies from 100 pg, 100 µl of 1,000 µl plated: 2 × 10⁶ cfu/µg), https://www.neb.com/en-us/faqs/how-should-i-calculate-the-transformation-efficiency-c2925: TE = Colonies/µg/Dilution.
4. find = col, te = 100,000,000, dna = 10, u = pg, how = frac, f = 0.1 gives expected = 100, result = 100 colonies expected. Source: NEB, FAQ: How should I calculate the transformation efficiency (C2925)? (TE = Colonies/µg/Dilution; 20 colonies from 100 pg, 100 µl of 1,000 µl plated: 2 × 10⁶ cfu/µg), https://www.neb.com/en-us/faqs/how-should-i-calculate-the-transformation-efficiency-c2925, the equation solved for the colonies.

## FAQ

### How do I calculate transformation efficiency?

Divide the colonies by the micrograms of DNA transformed and by the fraction of the transformation that you plated. NEB’s example: 100 pg (0.0001 µg) of pUC19, 50 µL of cells plus 950 µL of SOC, 100 µL plated (a fraction of 0.1), 20 colonies: 20 ÷ 0.0001 ÷ 0.1 = 2 × 10⁶ cfu/µg.

### What is the dilution in the formula?

The share of the DNA that ended up on the plate: the product of each step’s fraction. In NEB’s second example, 10 µL of the 300 µL recovery was taken up to 1 mL and 30 µL of that was plated: 10/300 × 30/1000 = 0.001. On this page, type 300 µL total, a dilution of 1 in 100 and 30 µL plated, or type the fraction 0.001.

### Why convert the DNA to micrograms?

Efficiency is quoted per microgram, though far less DNA is used: 100 pg is 0.0001 µg and 1 ng is 0.001 µg. The page converts picograms and nanograms for you.

### What is a good transformation efficiency?

It depends on the cells and the method. Ligation reactions give roughly 10-fold fewer transformants than an intact control plasmid (Addgene), and chemically competent cells take up large plasmids less well. Compare efficiencies only between runs done the same way.

### How many colonies will I get?

Multiply the efficiency by the micrograms of DNA and by the fraction plated. Cells at 1 × 10⁸ cfu/µg with 10 pg of plasmid and a tenth of the transformation plated give 10⁸ × 0.00001 × 0.1 = 100 colonies.

### Should I count every plate?

Count a plate with separate colonies, then give the fraction of the transformation on that plate. Addgene suggests plating 50 µL on one plate and the rest on a second, so at least one plate has single colonies.

## Sources

- NEB, FAQ: How should I calculate the transformation efficiency (C2925)?: TE = Colonies/µg/Dilution, with 100 pg, 50 µL of cells, 950 µL of SOC, 100 µL plated and 20 colonies giving 2 × 10⁶ cfu/µg. https://www.neb.com/en-us/faqs/how-should-i-calculate-the-transformation-efficiency-c2925 (retrieved 2026-10-19)
- NEB, FAQ: How should I calculate the transformation efficiency (C3040)?: dilution 10/300 × 30/1000 = 0.001, 150 colonies from 100 pg giving 1.5 × 10⁹ cfu/µg. https://www.neb.com/en-us/faqs/how-should-i-calculate-the-transformation-efficiency (retrieved 2026-10-19)
- Addgene, Protocol: Bacterial Transformation: 1 to 5 µL of DNA (10 pg to 100 ng) into 20 to 50 µL of cells, 250 to 1,000 µL of SOC, plating 50 µL and the rest, ligations about 10-fold less efficient. https://www.addgene.org/protocols/bacterial-transformation/ (retrieved 2026-10-19)