acalculator

What is transformation efficiency?

Enter the colonies you counted, the DNA you transformed, and how much of the transformation went on the plate. The calculator gives the transformation efficiency in colony-forming units per microgram of DNA, or the colonies to expect from cells of a known efficiency.

Your numbers

Find
DNA unit
Share plated from
Answer
TE = 2 × 10⁶ cfu/µg

TE = 2 × 10⁶ cfu/µg.

Transformation efficiency (cfu/µg)
2,000,000
DNA transformed (µg)
0.0001
Fraction plated
0.1
DNA on the plate (µg)
0.00001

Answer: TE = 2 × 10⁶ cfu/µg. TE = 2 × 10⁶ cfu/µg.

How to calculate

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.

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.

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.

  • 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.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Find Efficiency, Colonies counted 20, DNA transformed 100, DNA unit pg, Share plated from Volumes, Total volume after recovery (µL) 1,000, Volume plated (µL) 100 gives Transformation efficiency (cfu/µg) 2,000,000, Fraction plated 0.1, DNA on the plate (µg) 0.00001, Answer 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 Efficiency, Colonies counted 150, DNA transformed 100, DNA unit pg, Share plated from Volumes, Total volume after recovery (µL) 300, Extra dilution before plating (1 in …) 100, Volume plated (µL) 30 gives Transformation efficiency (cfu/µg) 1,500,000,000, Fraction plated 0.001, Answer 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 Efficiency, Colonies counted 50, DNA transformed 1, DNA unit ng, Share plated from A fraction, Fraction of the DNA plated 0.05 gives Transformation efficiency (cfu/µg) 1,000,000, DNA on the plate (µg) 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 Expected colonies, Efficiency (cfu/µg) 100,000,000, DNA transformed 10, DNA unit pg, Share plated from A fraction, Fraction of the DNA plated 0.1 gives Expected colonies 100, Answer 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

How it works

Efficiency (NEB).

TE = colonies ÷ µg of DNA ÷ fraction plated

  • µg of DNA: the amount typed, with 1 pg = 0.000001 µg and 1 ng = 0.001 µg.
  • Fraction plated (NEB’s “dilution”), from volumes: volume plated ÷ (total volume after recovery × extra dilution). The total volume is the cells plus the recovery medium. The extra dilution is “1 in x” for a further dilution of the recovered cells before plating (100 for 10 µL taken up to 1 mL; 1, the default, for none; an empty box counts as 1). Or type the fraction itself.
  • Expected colonies: colonies = TE × µg of DNA × fraction plated.

The page also gives the DNA in µg, the fraction plated, and the DNA on the plate (µg × fraction plated).

Rules the page checks.

  • Colonies are whole numbers from 0 to 1,000,000,000.
  • DNA from 0.000001 to 1,000,000,000 in its unit; the efficiency from 0.000001 to 10¹⁵ cfu/µg.
  • Volumes from 0.001 to 1,000,000 µL; the extra dilution from 1 to 1,000,000,000; a typed fraction from 10⁻¹² to 1.
  • The fraction plated cannot be above 1 (a volume plated larger than the volume it comes from): the page gives no answer.

How results are written. Every result is worked exactly from the typed decimals and rounded once, to 6 significant figures with trailing zeros dropped. The efficiency in the sentence is written m × 10ⁿ from 1,000 up (TE = 2 × 10⁶ cfu/µg, TE = 3.33333 × 10⁵ cfu/µg) and plainly below 1,000 (TE = 0 cfu/µg for no colonies), but m × 10ⁿ below 0.000001 (TE = 1 × 10⁻⁹ cfu/µg for 1 colony from 10⁹ µg). Expected colonies are written plainly with thousands commas (100 colonies expected, 123,457,000 colonies expected); below 0.000001 or from 10²¹ as m × 10ⁿ (1 × 10²⁴ colonies expected). A count that rounds to 1 reads “1 colony expected”.

Assumptions. Each colony on the counted plate grew from one transformed cell, and the plate is countable. As in NEB’s examples, the few µL of DNA added to the cells are left out of the total volume.

Worked examples by hand

NEB, 100 pg control plasmid. 100 pg = 0.0001 µg. Fraction plated = 100 ÷ 1,000 = 0.1. TE = 20 ÷ 0.0001 ÷ 0.1 = 2 × 10⁶ cfu/µg; the plate held 0.0001 × 0.1 = 0.00001 µg of DNA.

NEB, with a dilution step. Fraction plated = 30 ÷ (300 × 100) = 0.001 (NEB: 10/300 × 30/1000). TE = 150 ÷ 0.0001 ÷ 0.001 = 1.5 × 10⁹ cfu/µg.

A typed fraction. 1 ng = 0.001 µg, fraction 0.05, 50 colonies: TE = 50 ÷ 0.001 ÷ 0.05 = 1 × 10⁶ cfu/µg.

Expected colonies. 10 pg = 0.00001 µg at 1 × 10⁸ cfu/µg with 0.1 plated: 10⁸ × 0.00001 × 0.1 = 100 colonies.

Other questions people ask

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.