Frank Drake wrote the equation in 1961 for the first SETI meeting. It multiplies how often stars form by the chances of planets, life, intelligence and communication, and by how long civilizations remain detectable.
How to use the Drake Equation Calculator
- Star formation rate R* (per year)
- Fraction of stars with planets f_p
- Habitable planets per system n_e
- Fraction developing life f_l
- Fraction developing intelligence f_i
- Fraction that communicate f_c
- Communicating lifetime L (years)
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter each factor. Only R* and f_p are known reasonably well today.
Inputs explained
| Field | What to enter |
|---|---|
| Star formation rate R* (per year) | A number |
| Fraction of stars with planets f_p | A number |
| Habitable planets per system n_e | A number |
| Fraction developing life f_l | A number |
| Fraction developing intelligence f_i | A number |
| Fraction that communicate f_c | A number |
| Communicating lifetime L (years) | A number |
What each result means
- Number of civilizations N = [Star formation rate R× (per year)]×[Fraction of stars with planets f_p]×[Habitable planets per system n_e]×[Fraction developing life f_l]×[Fraction developing intelligence f_i]×[Fraction that communicate f_c]×[Communicating lifetime L (years)]
- New communicating civilizations per year = [Star formation rate R× (per year)]×[Fraction of stars with planets f_p]×[Habitable planets per system n_e]×[Fraction developing life f_l]×[Fraction developing intelligence f_i]×[Fraction that communicate f_c]
Example values
How the main result changes when Star formation rate R* changes and everything else stays at the example values above:
| Star formation rate R* (per year) | Number of civilizations N |
|---|---|
| 0.75 | 1.5 |
| 1.13 | 2.25 |
| 1.5 | 3 |
| 1.88 | 3.75 |
| 2.25 | 4.5 |
| 3 | 6 |
Formula
N = R*·f_p·n_e·f_l·f_i·f_c·L
Worked example
Inputs — Star formation rate R* (per year): 1.5; Fraction of stars with planets f_p: 1; Habitable planets per system n_e: 0.2; Fraction developing life f_l: 0.1; Fraction developing intelligence f_i: 0.1; Fraction that communicate f_c: 0.1; Communicating lifetime L (years): 10,000.
Results — Number of civilizations N = 3; New communicating civilizations per year = 0.0003.
Key terms
- SETI
- Search for extraterrestrial intelligence.
Frequently asked questions
What is the most uncertain factor?
f_l, f_i and L – we have only one example of life.
What did Drake estimate?
His group's original guesses gave between 1,000 and 100,000,000.
Does N = 1 mean we are alone?
Then we would be the only one – us.
Why does L matter so much?
Civilizations must overlap in time to detect each other.