Dark Sky Calculator

MSA ↔ Bortle

Approximate MSA/SQM → Bortle conversion using the SQM ranges shown in the English Wikipedia Bortle table. Decimal values (0.1 steps) are interpolated estimates; official Bortle classes are categorical.

Sky brightness (MSA / SQM)

mag/arcsec²

16 · bright1922 · dark

Approximate result

Bortle 3

Reverse conversion: Bortle → typical MSA

Approximate ranges

Bortle	MSA / SQM

Ranges through Bortle 8 follow the English Wikipedia table, including class 4.5. For this calculator, Bortle 9 is additionally anchored at approximately 17.5 mag/arcsec². Decimal values are interpolated between the boundaries.