What Is the Kardashev Scale? Types I, II and III Explained

Quick answer

The Kardashev scale ranks a civilisation by how much power it commands: Type I uses the energy of a whole planet, Type II the full output of its star and Type III that of a galaxy. On Carl Sagan's continuous version, humanity's roughly 21 terawatts rate about 0.73, well short of Type I.

📘 Full definition✓ Reviewed 2026-10-20

The Kardashev scale ranks a civilisation by the amount of power it commands. The Soviet astronomer Nikolai Kardashev proposed it in 1964, while working out how strong a radio signal another civilisation might be able to send. He described three types: Type I commands energy on the scale of its home planet, Type II the entire output of its star, and Type III the output of a whole galaxy. In 1973 Carl Sagan turned the three types into a continuous rating, so that any civilisation gets a number: Type I sits at 10¹⁶ watts, every tenfold rise in power adds 0.1, and each whole step is ten billion times more power than the one below. On that rating humanity, using about 21 terawatts of primary energy in 2025, scores about 0.73, and the figure creeps up by well under a thousandth a year. Nearly all of that power is used on the ground. A small but fast-growing share works in Earth orbit, where the solar arrays of thousands of satellites, most of them in mega-constellations in low Earth orbit, turn sunlight into electricity and go dark each time they pass through Earth's shadow. Space is also where a Type II civilisation would have to work, collecting its star's light far from any planet's surface.

Type I

10,000 terawatts

a planet's worth of power

Type II

A star's output

the Sun gives out about 380 trillion terawatts

Type III

A galaxy's output

ten billion times Type II

Humanity

About 0.73

some 21 terawatts in 2025

Understanding Kardashev Scale

Kardashev's types and Sagan's numbers

Kardashev pinned each type to a power level of his own: Type I at about 4 × 10¹² watts, close to Earth's whole energy use at the time, Type II at about the Sun's output and Type III at about that of the Milky Way. On his own numbers humanity already counted as Type I in 1964; it is Sagan's rounder and much higher bar, now the version most people quote, that leaves us at 0.73. The steps are so large that the scale only works on a logarithmic axis: humanity's energy use has grown more than fourfold since the 1960s, and that moved its rating by less than a tenth.

Type	Sagan's rating	Power	Kardashev's 1964 figure
Type I	1.0	10¹⁶ W	about 4 × 10¹² W
Type II	2.0	10²⁶ W	about 4 × 10²⁶ W
Type III	3.0	10³⁶ W	about 4 × 10³⁷ W
Humanity, 2025	about 0.73	about 2 × 10¹³ W	past Type I

The information axis

Sagan also suggested a letter for how much information a civilisation holds, starting from A for a million bits, with each letter ten times the one before. He put humanity of the early 1970s at about H, ten trillion bits, and called it a 0.7 H civilisation. Computing has since become one of the fastest-growing uses of energy, on the ground and, in a small way, in orbit, where the first satellites built to run artificial intelligence are now flying.

Power in orbit

The solar arrays working in Earth orbit add up to a few hundred megawatts, less than a ten-thousandth of humanity's energy use, and none of it reaches the ground: it runs the satellites themselves. It matters as a direction rather than an amount. The total has roughly doubled every year or two since 2019 as broadband constellations have grown, it rises with every launch and falls with every re-entry, and planned orbital data centres would add far more. The Kardashev Scale Tracker follows it live, alongside humanity's overall rating.

Frequently Asked Questions

Where is humanity on the Kardashev scale? ▼

About 0.73 on Carl Sagan's continuous version. Humanity used roughly 21 terawatts of primary energy in 2025, while Type I starts at 10,000 terawatts, nearly 500 times as much. With energy use growing by around 1 to 2 per cent a year, the rating rises by well under a thousandth a year.

Is the Kardashev scale a real measurement? ▼

It is a thought experiment rather than a unit anyone measures with. Kardashev proposed it in 1964 to estimate how powerful a signal other civilisations might send, and Sagan's formula simply turns power into a rating. It ignores efficiency, so a society that does more with less energy scores lower, and it says nothing about how the energy is used.

What would a Type II civilisation look like? ▼

It would collect most of the light its star gives out, which for the Sun is about 380 trillion terawatts. The usual picture is a Dyson swarm, a vast cloud of solar collectors orbiting the star. Astronomers have searched for the waste heat such a swarm would give off, an excess of infrared light from otherwise ordinary stars, so far without a confirmed detection.

Does the power of satellites count towards the Kardashev scale? ▼

Yes, it is part of humanity's total, but a tiny part: the solar arrays working in Earth orbit add up to a few hundred megawatts, less than a ten-thousandth of humanity's energy use. It is watched for its direction rather than its size, since a Type II civilisation would collect starlight in space.

Understanding Kardashev Scale

Kardashev's types and Sagan's numbers

The information axis

Power in orbit

Frequently Asked Questions

Sources & References