Exoplanet Transit SNR Calculator

Gauge whether a planned exoplanet transit is detectable with your setup. Provide the host-star and planet radii plus your per-exposure noise, optionally stack multiple transits, and receive a dimensionless SNR to compare against detection thresholds.

Host-star radius expressed in solar radii (R☉).
Planetary radius in Earth radii (R⊕).
Per-exposure photometric scatter in parts per million (ppm).
Leave blank for a single captured transit; enter 2 or more for multi-night stacks.
If left empty, the calculator uses 180 usable exposures per transit.

Outputs ignore red noise sources such as guiding drift or differential extinction.

Examples

  • Hot Jupiter around a Sun-like star with two stacked transits and 220 exposures each ⇒ SNR ≈ 552.90
  • Super-Earth orbiting an M dwarf with 150 exposures per transit across three nights ⇒ SNR ≈ 144.42

FAQ

What SNR indicates a confident transit detection?

Amateur observers typically aim for transit SNR above 7–10 to claim a detection, while pro-am databases prefer submissions closer to 15 or higher for robust vetting.

How do ingress and egress points affect the calculation?

The model assumes every exposure is fully in-transit. If you include ingress or egress frames, the true SNR will be a bit lower because those points are only partially attenuated.

Can I mix data from different nights?

Yes. Set "Number of transits stacked" to the total nights you plan to co-add, but make sure each light curve is detrended and normalized before stacking.

What if my noise is expressed in millimagnitudes?

Convert millimagnitudes to ppm by multiplying by 921. Example: 0.5 mmag corresponds to roughly 460 ppm before entering it here.

Additional Information

  • Transit depth follows (Rp/Rs)², with Earth radii converted to solar radii before squaring.
  • Noise input should combine photon shot noise, scintillation, and instrumental scatter measured per exposure in ppm.
  • The calculator multiplies stacked frames and transits, boosting SNR with the square root of the total number of usable exposures.
  • Systematic noise sources (red noise, weather trends, or detrending errors) are not included—treat high SNR values as optimistic.

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