Does PERF_IMAGE_DIMENSIONS affect my score?

Yes. It is an importance 6 rule at SPECIFICATION confidence, so a failure costs 6 × 1 points of impact in the Performance category before that category is normalised to 100.

What does SPECIFICATION confidence mean?

A standard says so: HTML, WCAG, an RFC or Google's own documentation. Confidence is a declared tier rather than a per-rule number, so every rule backed by the same class of evidence carries the same weight - which is what makes the score reproducible instead of hand-tuned.

How do I check PERF_IMAGE_DIMENSIONS on my own site?

Paste your URL into the box above and it runs only this rule, usually in a couple of seconds. It is also included in the Performance checker and in a full scan.

PerformanceMedium Affects your score

Images declare width and height

PERF_IMAGE_DIMENSIONS

An <img> without intrinsic dimensions occupies zero height until it loads, then pushes everything below it down. Declaring width and height lets the browser reserve the space up front, which is the primary fix for layout shift.

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How this rule is weighted

Importance: 6 / 10; How much this matters relative to other rules.
Confidence: SPECIFICATION; A standard says so: HTML, WCAG, an RFC or Google's own documentation.
Severity: warning; How the finding is presented when it fails.
Scoring: Counts; A failure costs points in its category.

Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.

Questions about this rule

Does PERF_IMAGE_DIMENSIONS affect my score?: Yes. It is an importance 6 rule at SPECIFICATION confidence, so a failure costs 6 × 1 points of impact in the Performance category before that category is normalised to 100.
What does SPECIFICATION confidence mean?: A standard says so: HTML, WCAG, an RFC or Google's own documentation. Confidence is a declared tier rather than a per-rule number, so every rule backed by the same class of evidence carries the same weight - which is what makes the score reproducible instead of hand-tuned.
How do I check PERF_IMAGE_DIMENSIONS on my own site?: Paste your URL into the box above and it runs only this rule, usually in a couple of seconds. It is also included in the Performance checker and in a full scan.

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