Convert Dots per pixel to Pixels per inch

Convert Dots per pixel (dppx) to Pixels per inch (PPI) instantly and accurately.

Conversion Formula

PPI = dppx × 96

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 Pixels per inch

The pixel per inch (PPI) is the universal standard for digital image resolution, defining how many pixels occupy one linear inch in a digital image, sensor, or display. Formally referenced in ISO 12232 (digital still cameras) and EXIF/TIFF (tags 0x011A/0x011B), PPI is both a capture parameter (scanner/sensor density) and a display characteristic. Display milestones: Macintosh 128K (1984): 72 PPI; Apple iPhone 4 Retina (2010): 326 PPI - above the human perceptual threshold at 25 cm; iPhone 15 Pro (2023): 460 PPI. Print benchmarks: 150 PPI (large-format, 1 m viewing); 300 PPI (standard offset, ISO 12647-2); 400-600 PPI (fine-art Giclée). EXIF stores PPI as unsigned RATIONAL; the historical default is 72/1, a carry-over from the original Macintosh screen standard. 1 PPI = 1/0.0254 px/m ≈ 39.37 px/m = 2.54 px/cm.

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