Sizu Riatto
Every Angle · Chapter 6

Pixels per Meter

Whether a camera can show a face is one rearranged formula. Pixels per meter falls as the view widens; solve it for distance and you know where the camera stops being useful.

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Opens on the book's house and plot. Change any number to your own and press Calculate.

Enter the camera's pixels and field of view, then press Calculate.

The formula

  • The width of the view at distance d = 2 × d × tan(field of view ÷ 2)
  • Pixel density (px/m) = horizontal pixels ÷ the width of the view
  • Rearranged for distance: d = pixels ÷ (2 × density × tan(field of view ÷ 2))
  • IEC 62676-4 (DORI): identify 250 px/m, recognize 125, observe 62.5, detect 25. 250 px/m puts 40 px across a 16 cm face
The book's worked example, Chapter 6. A typical 4 MP camera, 2,560 px wide behind a 2.8 mm lens, 100° wide: identify to 4.30 m (14.1 ft), recognize to 8.59 m, observe to 17.18 m, detect to 42.96 m. At the identify reach the view is 10.24 m wide. The doorbell, 1,920 px and 140°, gives a caller 1.0 m away 349.4 px/m; it identifies out to 1.40 m.
Check it. Stand a friend at the distance, record, and count the pixels across their face on a still: 40 px or more across a 16 cm face is identify.

Honest limits. Datasheet DORI distances for wide lenses often run about 30% longer than this formula: treat them as a best case and compute your own. Night, rain, glare and compression all lower the detail you really get. The book's house was worked out on paper from published figures, not surveyed by us: measure your own, and walk your own plot at night. Prices are illustrative US prices from November 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.

These calculators go with Every Angle (Make It Add Up, Book 2), where every number on this page is worked by hand.