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
The perfect companion for Bortle 1-3 skies. Smart imaging that ignores light pollution.
Acquire UnitThe Dossier
Stargazer's Blueprint
Master the Bortle Scale with our 40-page technical guide.
Understanding 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.
Our calculator uses standard astronomical conversion formulas to estimate SQM and NELM based on the Bortle class. While individual conditions like atmospheric transparency (humidity) and aerosol levels can shift these numbers slightly, this table provides the authoritative baseline for planning your next observing session.
Read our full guide to Bortle classes