Convert Dots per pixel to Lines per millimetre

Convert Dots per pixel (dppx) to Lines per millimetre (lp/mm) instantly and accurately.

Conversion Formula

lp/mm = dppx × 3.779527559

About Dots per pixel

The dot per CSS-pixel unit (dppx, or the x descriptor in CSS) is defined in W3C CSS Images Level 3 / Media Queries Level 4 as the ratio of physical device pixels to CSS reference pixels, where the CSS spec fixes 1 CSS inch ≡ 96 CSS px exactly. Therefore 1 dppx = 96 DPI = 96 PPI exactly; a screen reporting device pixel ratio (DPR) of 2 has 2 dppx = 192 physical dots per CSS inch. JavaScript exposes DPR as window.devicePixelRatio, numerically equal to dppx. Reference values: standard laptop (96-110 PPI): 1 dppx; MacBook Pro 13-inch Retina (227 PPI): 2 dppx; iPhone 15 Pro 6.1-inch (460 PPI): 3 dppx; Samsung Galaxy S24 Ultra (501 PPI): ≈ 3.09 dppx. The HTML img srcset x descriptor (photo@2x.jpg 2x) is numerically equal to dppx, serving higher-resolution images for HiDPI screens. The CSS @media (min-resolution: 2dppx) query targets any display with DPR ≥ 2. 1 dppx = 96 DPI = 96 PPI.

About Lines per millimetre

The line pair per millimetre (lp/mm) is the fundamental unit of spatial resolution in classical optics, characterising the resolving power of a lens, film emulsion, sensor, or microscope objective. A resolving power of N lp/mm means adjacent line pairs separated by 1/(2N) mm can be distinguished - derived from the Abbe diffraction limit (Ernst Abbe, 1873) and Rayleigh criterion (Lord Rayleigh, 1879). Film benchmarks at MTF50: Kodak Tri-X 400: 63 lp/mm; Fujifilm Velvia 50: 160 lp/mm; Kodak Technical Pan: 320 lp/mm. Lens benchmarks: Leica APO-Summicron-M 50 mm f/2 ASPH: ≈ 75 lp/mm at centre. CMOS sensor Nyquist frequency: for pixel pitch p mm, f_Nyquist = 1/(2p) lp/mm - a 4.63 µm pixel limits at ≈ 108 lp/mm. As a dimensional unit, 1 lp/mm = 25.4 LPI = 25.4 PPI exactly. 1 lp/mm = 25.4 PPI.

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