Pixel Scale Calculator

What the Pixel Scale Calculator Does

This pixel scale calculator tells you how much sky each pixel of your camera covers when paired with a specific telescope or lens, measured in arcseconds per pixel (arcsec/px). You enter your sensor's pixel size in microns and your optical system's focal length in millimeters, and it returns the imaging resolution of that combination.

It's built for astrophotographers choosing or matching gear: deep-sky imagers checking whether a camera suits a refractor, planetary shooters tuning a Barlow setup, and anyone deciding between two cameras for the same scope. Knowing your arcsec per pixel value helps you predict how detailed and how 'sampled' your images will be before you spend a night under the stars.

How It Works: The Pixel Scale Formula

Pixel scale comes from simple trigonometry of small angles. One pixel subtends a tiny angle on the sky, and the formula converts that angle into arcseconds:

pixel scale (arcsec/px) = 206.265 × pixel size (µm) / focal length (mm)

The constant 206,265 is the number of arcseconds in one radian. Because pixel size is given in microns and focal length in millimeters, the units work out so the result lands directly in arcseconds per pixel. Larger pixels or shorter focal lengths give a bigger (coarser) scale; smaller pixels or longer focal lengths give a finer scale.

Worked Example With Real Numbers

Suppose you own a camera with 3.76 µm pixels (a common APS-C and mono sensor size) and a refractor with a 600 mm focal length. Plug the values in:

pixel scale = 206.265 × 3.76 / 600 = 775.56 / 600 = 1.29 arcsec/px

A result of 1.29 arcsec/px falls neatly in the well-sampled range, so this pairing is a good match for typical deep-sky work. If you added a 2x Barlow, the focal length becomes 1200 mm and the scale halves to about 0.65 arcsec/px, pushing you into oversampling unless your skies and tracking are excellent.

Reading the Result: Sampling Ranges

The arcsec per pixel value tells you whether your setup is matched to typical seeing conditions:

• Roughly 1 to 2 arcsec/px: well sampled, the sweet spot for most deep-sky imaging.
• Below 1 arcsec/px: oversampled, where each star is spread over many pixels, dimming the signal per pixel and demanding very steady seeing and tracking.
• Above 2 arcsec/px: undersampled, where fine detail is lost and stars can look blocky, though this gives a wider field and brighter per-pixel signal.

Tips, Common Mistakes, and Factors That Affect Results

These ranges are guidelines, not hard rules. The 'ideal' scale depends on your sky: under typical 2 to 4 arcsec seeing, aiming below about 1 arcsec/px rarely captures extra real detail because the atmosphere, not your pixels, sets the limit. Planetary imagers deliberately oversample (using lucky imaging to beat seeing), so they break these rules on purpose.

Watch for these frequent errors:

• Using physical focal length while ignoring a reducer or Barlow. Always use the effective focal length of the whole optical train.
• Confusing pixel size with sensor size, or mixing up binned versus native pixels. 2x2 binning doubles the effective pixel size and the scale.
• Forgetting units. Pixel size must be in microns and focal length in millimeters for the 206.265 constant to apply.
• Treating the field of view as the same thing as pixel scale; field of view also depends on sensor width and height, not just one pixel.