Habitable Zone Calculator
Estimate the inner and outer edges of a star's circumstellar habitable zone from its luminosity.
Lsun
Rsun
K
Based on luminosity 1 Lsun
- 1
Luminosity (Lsun)
1 Lsun - 2
Inner habitable-zone edge
√(1 ÷ 1.1) = 0.953 AU - 3
Outer habitable-zone edge
√(1 ÷ 0.53) = 1.374 AU - 4
Zone center
(0.953 + 1.374) ÷ 2 = 1.164 AU
How does this calculator work?
A star's habitable zone spans roughly sqrt(L/1.1) AU (inner) to sqrt(L/0.53) AU (outer), where L is luminosity in solar units. For a Sun-like star (L = 1) that is about 0.95 to 1.37 AU. Enter luminosity directly, or derive it from the star's radius and temperature via the Stefan-Boltzmann law.
Formula
How this is calculated
The habitable zone (or "Goldilocks zone") is the range of orbital distances around a star where the stellar flux reaching a planet allows liquid water to exist on its surface. Because received flux falls off as the inverse square of distance, the zone edges scale with the square root of the star's luminosity L (in solar luminosities, Lsun). This calculator uses simple flux-bound estimates: the inner edge at sqrt(L / 1.1) AU (the runaway-greenhouse / too-hot limit) and the outer edge at sqrt(L / 0.53) AU (the maximum-greenhouse / too-cold limit). The reported center is the midpoint of these two edges.
You can enter the luminosity directly, or leave it blank and supply the star's radius (in solar radii) and surface temperature (in Kelvin). In that case luminosity is derived from the Stefan-Boltzmann law, L = 4 pi R^2 sigma T^4, then divided by the Sun's luminosity (3.828e26 W) to express it in Lsun. Radius is converted from solar radii using R_sun = 6.957e8 m and sigma = 5.67e-8 W m^-2 K^-4.
Assumptions: the flux coefficients 1.1 and 0.53 are constant approximations and do not account for the host star's spectral type, planetary albedo, atmosphere, or greenhouse composition, so treat the result as a first-order estimate. Inputs must be positive; non-positive luminosity, radius, or temperature returns no result.
Frequently asked questions
Stellar flux drops with the square of distance (flux is proportional to L / d^2). Holding the flux limit constant and solving for distance gives d proportional to sqrt(L), so both edges scale with the square root of the luminosity.
Yes. Leave the luminosity field blank and enter radius (in solar radii) and surface temperature (in Kelvin). The calculator computes luminosity from the Stefan-Boltzmann law L = 4 pi R^2 sigma T^4 and converts it to solar units before finding the zone edges.
They are order-of-magnitude estimates using simple flux bounds. Real habitable-zone limits depend on stellar spectrum, planetary albedo, atmospheric pressure, and greenhouse gases, so detailed climate models give somewhat different edges.
Also known as
TG we-Calculate Editorial Team. (2026). Habitable Zone Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/habitable-zone-calculator
TG we-Calculate Editorial Team. "Habitable Zone Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/habitable-zone-calculator.
TG we-Calculate Editorial Team, "Habitable Zone Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/habitable-zone-calculator
@misc{wecalculate_habitable_zone_calculator, title = {Habitable Zone Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/habitable-zone-calculator}}, year = {2026}, note = {TG we-Calculate} }
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