Free Astro Pixel Scale Calculator
Pixel scale is the angular size of one sensor pixel on the sky, measured in arcseconds per pixel — the number that decides whether your camera can resolve stars. Image scale = 206.265 × pixel size (µm) ÷ focal length (mm). The result, in arcseconds per pixel, tells you whether your seeing, tracking, and optics are matched to your sensor.
Your setup
Result
Why pixel scale matters
Pixel scale determines how much sky each pixel covers. It's the single best number for judging whether a camera + lens/telescope pairing makes sense before you buy:
- Undersampled (> 3–4″/px): stars land on single pixels — square, blocky stars that don't improve with more exposure.
- Sweet spot (1–2″/px): several pixels across each star image; good for most mounts and skies.
- Oversampled (< 0.7″/px): the optics or seeing can't deliver that detail — you collect noise and huge files for nothing, and tracking errors become visible.
Rule of thumb: pixel scale ≈ seeing ÷ 3 gives near-critical sampling. With 2″ seeing that's ~0.67″/px — most hobbyists choose slightly coarser to keep guiding easy.
Related tools & guides
Star Trails Calculator
NPF / 500 / 300 / 600 rule exposure times.
Open →Field of View Calculator
How much sky your camera + lens sees.
Open →Hyperfocal Distance Chart
The focus distance that maximizes sharp depth.
Open →Pixel scale FAQ
What's the formula for pixel scale?
Pixel scale (″/px) = 206.265 × pixel size (µm) ÷ focal length (mm). Example: a camera with 3.8 µm pixels behind a 400 mm lens gives 206.265 × 3.8 ÷ 400 ≈ 1.96″/px.
Is smaller pixel scale always better?
No. Below the seeing limit you're oversampling — more pixels per star than the atmosphere delivers. The result is larger files, longer exposures for the same signal, and stricter guiding for zero real resolution gain.
How do I find my camera's pixel size?
Pixel size = sensor height (mm) × 1000 ÷ vertical resolution. ShutterMath stores this for every camera in the list automatically — just pick your camera.