Light Pollution Calculator

Estimate naked-eye and telescope limiting magnitude and SQM reading based on Bortle class, altitude, and moon phase.

Bortle Class (1-9)

Altitude (ft)

Moon Phase (%)

Tab to move between fields

Naked-Eye Limit

5.6 mag

Telescope Limit (8")

12.9 mag

SQM Reading20.49 mag/arcsec²

How to Use This Calculator

Enter Bortle Class (1-9), Altitude (ft), and Moon Phase (%).
Review Naked-Eye Limit (mag) and Telescope Limit (8 (mag).
Use SQM Reading (mag/arcsec²) to inform your decision.
Use the chart to visualize the results and explore different scenarios by adjusting inputs.

What each input means

Bortle Class (1-9): Light pollution level: 1 = excellent dark site, 5 = suburban, 9 = inner city
Altitude (ft): Your elevation above sea level in feet (higher = cleaner air)
Moon Phase (%): Moon illumination percentage (0% = new moon, 100% = full moon)

Identify Input Parameters
Bortle Class (1-9) + Altitude (ft) + Moon Phase (%)
Bortle Class (1-9) = 5, Altitude (ft) = 1000, Moon Phase (%) = 0 = 3 input(s) provided
Calculate Naked-Eye Limit
Naked-Eye Limit
5.6 = 5.6
Calculate Telescope Limit (8
Telescope Limit (8
12.9 = 12.9

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