BORTLE TO NAKED EYE
LIMIT CALCULATOR
Precision conversion between Bortle Class, Sky Quality Meter (SQM) readings, and Naked Eye Limiting Magnitude (NELM).
Magnitude (SQM)
22.00
mag/arcsec²
NELM Score
7.6
Visibility Limit
Observational Status
Professional research conditions. Airglow is visible.
Pro Intelligence
Recommended Gear
ZWO Seestar S50
A specification-led smart-telescope example for darker skies. Performance depends on target, exposure and actual conditions.
Research optionsThe Dossier
Stargazer's Blueprint
Master the Bortle Scale with our 40-page technical guide.
Find a Dark Sky
Use the interactive dark-sky coordinate map with geographic basemap; measured light-pollution Class 1 overlay is not yet active.
Launch MapUnderstanding the Bortle Scale
Created by John E. Bortle in 2001, the Bortle scale is a nine-level numeric scale used to measure the brightness of the night sky at a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution.
For serious astrophotographers and deep-sky observers, finding a location with a Bortle Class 1 or 2 sky is the single biggest factor in image quality—more important than the camera or telescope used.
This calculator gives a rough SQM and NELM range from a selected Bortle class. It is a planning estimate, not a measurement: transparency, aerosols, local lighting, eyesight and the map's source resolution can all change what you see.
Compare the dark-sky map