Convert Pixels per foot to Dots per pixel

Convert Pixels per foot (px/ft) to Dots per pixel (dppx) instantly and accurately.

Conversion Formula

dppx = px/ft × 0.0008680555556

About Pixels per foot

The pixel per foot (px/ft) is an imperial resolution unit used in architectural visualisation, large-format display engineering, and document scanning where distances are measured in feet. The foot is exactly 0.3048 m = 12 in (international foot, 1959), giving 1 px/ft = 1/12 PPI ≈ 0.08333 PPI. Microfilm scanners for engineering drawing digitisation (ANSI/AIIM MS23) are specified in px/ft; a 200 px/ft scan of a 24-inch D-size drawing yields 400 pixels across the 2-foot width. Outdoor LED walls at P6 pixel pitch (6 mm) covering one foot ≈ 50.8 px/ft. Building plans at 1:48 scale reduce 1 actual foot to 0.25 in on paper, requiring ≥ 3 px/ft for legibility. 1 px/ft = 1/12 PPI ≈ 0.083333 PPI ≈ 3.281 px/m.

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.

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