Schwarzschild Radius Calculator
Find the Schwarzschild radius — the event-horizon size of a black hole — directly from its mass.
Mass unit
Event-horizon radius of the black hole
- 1
Mass in kilograms
1 × 1.989 × 10³⁰ = 1.989 × 10³⁰ - 2
Numerator 2·G·M
2 × 6.674 × 10⁻¹¹ × 1.989 × 10³⁰ = 2.6549 × 10²⁰ - 3
Rs = 2·G·M ÷ c²
2.6549 × 10²⁰ ÷ 8.988 × 10¹⁶ = 2,953.8451
How does this calculator work?
The Schwarzschild radius is Rs = 2GM/c², the event-horizon size of a black hole of mass M. Enter the mass in kilograms, Earth masses, or solar masses to get the radius in meters, kilometers, and solar radii. One solar mass gives about 2.95 km.
Formula
How this is calculated
Enter the mass M of the object and choose its unit: kilograms, Earth masses (1 M⊕ = 5.972e24 kg), or solar masses (1 M☉ = 1.989e30 kg). The mass is converted to kilograms before the calculation.
The Schwarzschild radius is computed as Rs = 2GM/c², where G is the gravitational constant (6.674×10⁻¹¹ m³ kg⁻¹ s⁻²) and c is the speed of light (2.998×10⁸ m/s). This is the radius at which the escape velocity equals the speed of light, defining the event horizon of a non-rotating, uncharged (Schwarzschild) black hole. A handy shortcut is Rs ≈ 2.95 km × (M / M☉).
Results are reported in meters, kilometers, and solar radii (R☉ = 6.957×10⁸ m). The formula assumes a spherically symmetric mass and ignores rotation and charge. Mass must be positive; any object compressed within its Schwarzschild radius becomes a black hole.
Frequently asked questions
Using Rs = 2GM/c² with one solar mass gives roughly 2.95 km, meaning the Sun would have to collapse to about a 3 km radius to become a black hole.
No. This uses the Schwarzschild solution for a non-rotating, uncharged black hole. Rotating (Kerr) or charged (Reissner–Nordström) black holes have different horizon radii.
Yes. Rs scales linearly with mass, so doubling the mass doubles the radius. The shortcut Rs(km) ≈ 2.95 × (M / M☉) reflects this proportionality.
Also known as
TG we-Calculate Editorial Team. (2026). Schwarzschild Radius Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/schwarzschild-radius-calculator
TG we-Calculate Editorial Team. "Schwarzschild Radius Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/schwarzschild-radius-calculator.
TG we-Calculate Editorial Team, "Schwarzschild Radius Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/schwarzschild-radius-calculator
@misc{wecalculate_schwarzschild_radius_calculator, title = {Schwarzschild Radius Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/schwarzschild-radius-calculator}}, year = {2026}, note = {TG we-Calculate} }
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