Device Pixel Ratio CSS px Lookup
Matched actual CSS/device pixel extent ratio, not physical PPI or inferred fixed ratio for a devices name. Explicit caller font/layout/reference context; not a shaping engine, actual page layout or accessibility certification.
Description
Device pixel ratio compares matched device-pixel and CSS-pixel extents.
When to use Device Pixel Ratio CSS px Lookup
Use this tool when you need to reproduce the stated calculation from measured records or independently selected model inputs. Establish the font version, feature, layout, physical or CSS units, and matched reference basis needed for this calculation.
How to use Device Pixel Ratio CSS px Lookup and understand its results
- Establish the font version, feature, layout, physical or CSS units, and matched reference basis needed for this calculation.
- Enter observedDevicePixelExtent, observedMatchedCssPixelExtent, following the field table and rules below, then run the tool.
- Read observedDevicePixelRatio. Use the output meanings below to interpret units, signs, flags, and any nested result fields.
- Correct reported input issues and run again. For a successful result, check the stated evidence coverage and assumptions before using it in your review.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| observedDevicePixelExtent | Observed device pixel extent | number | Required |
| observedMatchedCssPixelExtent | Observed matched CSS pixel extent | number | Required |
Enter positive matched extents along the same axis and under the same display conditions. Divide device pixels by CSS pixels. No screen diagonal or model catalog is used.
DPR=devicePixelExtent/cssPixelExtent Symbols follow the input and output meanings and the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| observedDevicePixelRatio | Observed device pixel ratio | number |
{
"input": {
"observedDevicePixelExtent": 200,
"observedMatchedCssPixelExtent": 100
},
"output": {
"observedDevicePixelRatio": 2
}
}Limitations and assumptions
The calculation uses declared units and font or layout assumptions. It does not shape glyphs, lay out actual pages, or certify accessibility or print quality.
Missing required fields, unknown fields, wrong types, and violated calculation rules are input issues. Numeric values must be finite; nonfinite results are rejected.
Alternative or Complementary methods
For a related review, use Screen PPI From Diagonal Resolution: Physical screen PPI measures raster pixels per physical inch. It is distinct from a CSS pixel scale or the ratio between device and CSS pixels. For a complementary step, use Large Text 18pt/24px Threshold Classifier: WCAG large-text size categories use CSS-equivalent point thresholds and distinguish bold from regular text. This screen evaluates only that size category, which is one input to a contrast review.
References
Similar or alternative tools
- Screen PPI From Diagonal Resolution
Physical screen PPI measures raster pixels per physical inch. It is distinct from a CSS pixel scale or the ratio between device and CSS pixels.
- Large Text 18pt/24px Threshold Classifier
WCAG large-text size categories use CSS-equivalent point thresholds and distinguish bold from regular text. This screen evaluates only that size category, which is one input to a contrast review.