Drake equation calculator.
Seven numbers, multiplied, to estimate how many civilizations in our galaxy we could detect right now. Three have real measurements behind them. Four are guesses. Make yours.
Set the seven numbers.
Move a slider or type a value. Presets load published or illustrative values, and changing any number makes it your guess.
N = R* × fp × ne × fl × fi × fc × L
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How many new stars our galaxy makes each year, counted as stars, not by weight. Measured by mass: the Milky Way turns about 1.65 Suns’ worth of gas into stars a year (Licquia and Newman, 2015), and a count of young stars gives 0.68 to 1.45 (Robitaille and Whitney, 2010). Most new stars are red dwarfs far lighter than the Sun, so that mass makes roughly six to seven stars a year (Annette Ferguson, University of Edinburgh, 2022). Drake’s group used 1.
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The fraction of those stars that have planets, from 0 to 1. Measured: a 2012 survey found every star in the galaxy should have at least one planet on average (NASA). The NASA Exoplanet Archive listed 6,372 confirmed planets on September 25, 2026.
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How many planets in each system could hold liquid water on the surface. Measured for Sun-like stars: Kepler data give 0.37 to 0.60 rocky habitable-zone planets per star, and up to 0.88 on a looser definition (Bryson and colleagues, 2020; NASA summary).
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UnknownThe fraction of habitable planets where life actually appears. We have one example, Earth, so this is a guess. The slider moves in powers of ten.
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UnknownThe fraction of living worlds that produce intelligence. Also one example, also a guess.
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UnknownThe fraction of intelligent species that send out signals we could pick up, such as radio. A guess.
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UnknownHow many years a civilization keeps sending detectable signals. We have been sending radio for about a century, and nobody knows how long any civilization lasts.
Detectable civilizations in the Milky Way right now
20
Twenty civilizations.
Model Spread evenly through our model galaxy, a flat disc 100,000 light-years across and 1,000 thick, neighbours would sit about 20,000 light-years apart. A radio signal would take about 20,000 years to cross that gap one way.
Drake 1961: the low end of the ranges the 1961 Green Bank meeting agreed on.
The equation organizes what we do not know. It does not measure anything, and no number it gives is evidence either way.
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Sources
- The 1961 values: Frank Drake and Dava Sobel, Is Anyone Out There? (1992), pages 55 to 62. We checked these figures against published summaries of the book, not the book itself: R* 1, fp 0.2 to 0.5, ne 1 to 5, fl 1, fi 1, fc 0.1 to 0.2, L 1,000 to 100,000,000 years.
- Star formation by mass: Licquia and Newman, The Astrophysical Journal 806, 96 (2015), arXiv:1407.1078, 1.65 ± 0.19 solar masses a year; Robitaille and Whitney, The Astrophysical Journal Letters 710, L11 (2010), arXiv:1001.3672, 0.68 to 1.45.
- Star formation by count: Annette Ferguson, How many stars are born each year in the Milky Way?, Astronomy, November 21, 2022: one to two solar masses a year makes roughly six to seven stars.
- Planets per star: NASA, The Milky Way contains at least 100 billion planets (Cassan and colleagues, Nature, 2012).
- Habitable-zone planets: Bryson and colleagues, The occurrence of rocky habitable zone planets around solar-like stars from Kepler data, The Astronomical Journal.
- Confirmed planet count: NASA Exoplanet Archive, checked September 28, 2026.
- Uncertainty: Anders Sandberg, Eric Drexler and Toby Ord, Dissolving the Fermi Paradox, arXiv:1806.02404 (2018).
Pessimist and Optimist are our own illustrations of two outlooks, not published estimates. The neighbour distance and the 20,000 runs below are our own models, worked out on this page from the numbers you set.
One number hides the real uncertainty.
Every preset gives a single N. Four of the seven terms are unknown across many powers of ten, so any single N is mostly a statement about the guesses.
In 2018 Anders Sandberg, Eric Drexler and Toby Ord replaced each guess with a range as wide as the published estimates really are, then looked at the whole spread of answers instead of one. Their paper, Dissolving the Fermi Paradox, found a substantial chance that no other intelligent life exists in the observable universe. On that reading, a silent sky is no surprise.
That is a result about uncertainty, not a measurement of aliens. It says the equation cannot yet tell a crowded galaxy from an empty one.
Try it with your numbers
We keep your three measured terms and draw the four unknowns 20,000 times, each spread evenly across the powers of ten its slider covers: fl, fi and fc from one in a billion to 1, and L from 1 to 10 billion years.
Running the model needs JavaScript.
Model A simple model of the slider ranges, not a published estimate. Its answer depends on those ranges.
Where Earth sits on the Kardashev scale.
In 1964 the Soviet astronomer Nikolai Kardashev sorted civilizations into three types by the power they command. Carl Sagan later turned the types into a sliding number.
The Kardashev scale ranks a civilization by how much power it uses: Type I runs on a planet’s worth, Type II on a star’s, Type III on a galaxy’s. Earth rates about 0.73, because humanity uses around 19 trillion watts and Type I starts at 10,000 trillion.
1013.3 watts gives K = 0.73. That is about where humanity is today.
K = (log10 P − 6) ÷ 10
P is power in watts.
The world used just over 600 exajoules of primary energy in 2025, according to the Energy Institute’s 2026 Statistical Review of World Energy. Spread over a year that is about 19 trillion watts, or 1013.3, so K comes out near 0.73. A 2022 study using the same formula, with P in watts, got 0.728 from 2018 data (Jiang and colleagues, Galaxies; free copy on arXiv).
- Type I1016 watts: all the power available on a planet.
- Type II1026 watts: power on the scale of a whole star.
- Type III1036 watts: power on the scale of a whole galaxy.
The watt figures come from Sagan’s formula. Nobody has detected a civilization of any type.
Questions about the Drake equation.
What is the Drake equation?
A formula the astronomer Frank Drake wrote for a 1961 meeting at the Green Bank radio observatory in West Virginia. It multiplies seven factors to estimate N, the number of civilizations in our galaxy whose signals we could detect at any one time.
What numbers did Drake use in 1961?
As Drake recounted in his 1992 book with Dava Sobel, the meeting settled on ranges: one new star a year, a fifth to a half of stars with planets, one to five habitable planets per system, life and intelligence arising every time, 10 to 20 percent of those becoming detectable, and a lifetime of 1,000 to 100 million years. They concluded that N is roughly equal to L. The Drake 1961 preset uses the low end of each range.
Does the Drake equation prove aliens exist?
No. Three of its terms now have measurements behind them. The other four rest on one example: us. It is a way to organize the question. Separately, the official reviews of UAP reports so far, from AARO and NASA, found no evidence of extraterrestrial technology.
Where is Earth on the Kardashev scale?
At about 0.73. The world used just over 600 exajoules of primary energy in 2025, about 19 trillion watts on average. Sagan’s formula, K = (log10 P − 6) ÷ 10 with P in watts, turns that into 0.73. Type I would take roughly 500 times more power.
Why is R* about seven when the galaxy makes under two Suns of stars a year?
R* counts stars, and most new stars are red dwarfs much lighter than the Sun. The galaxy turns one to two solar masses of gas into stars a year, which works out to roughly six to seven stars. Drake’s 1961 group used one star a year.
What is a Type I civilization?
One that commands all the power available on its planet. On Sagan’s sliding version of Kardashev’s scale that is 1016 watts. Humanity sits near 0.73.
If the answer is ever more than one.
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