Convert your Sky Quality Meter reading to Bortle scale class and find the visual limiting magnitude for your observing site.
Take a reading with a Sky Quality Meter pointed at the zenith and enter the value in magnitudes per square arcsecond. Readings run from roughly 16–18 over cities to nearly 22 at pristine dark-sky sites; the converter accepts 15 to 22.
The conversion follows the canonical SQM-to-Bortle mapping: 21.99 or higher is Class 1, 21.25 keeps you within Class 4, and anything below 18.38 lands in Class 9, the brightest inner-city category.
Each class pairs with a naked-eye limiting magnitude from 7.6 down to 3.0, and the tool also reports whether the zodiacal light and the galaxy M33 should be visible without optics — both realistic only at Class 4 or darker.
A zenith reading of 21.99 mag/arcsec² or higher. This converter uses the canonical mapping found in dark-sky field guides, with Class 2 starting at 21.89, Class 3 at 21.69, Class 4 at 21.25, and Class 5 at 20.49.
The naked-eye limit runs from magnitude 7.6 at Class 1 down to 6.1 at Class 4, 5.6 at Class 5, and just 3.0 at Class 9. Each step toward brighter skies erases roughly half a magnitude of the faintest visible stars.
Both are indicators of genuinely dark skies, and this converter reports them as visible at Bortle Class 4 or darker. M33, the Triangulum Galaxy, is a classic naked-eye test object that disappears quickly as light pollution increases.
Point the meter straight up at the zenith on a clear, moonless night away from direct lights, and take several readings once the value stabilizes. Moonlight or thin haze brightens the sky and will skew the conversion toward a worse Bortle class.