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Free text zoom readability calculator. Get effective font size (px), a 0–100 readability score, and Low / Moderate / High level from base size, zoom %, and line length. Pair with font size accessibility for baseline typography.
Last updated: May 24, 2026
Testing 200% WCAG resize? Contrast ratio calculator
Effective Font Size
20px
Readability Score
76.6 / 100
Readability Level
High
Readability appears strong for the selected profile. Maintain current zoom and layout proportions.
Planning tool only. Validate final readability with real users and assistive technology testing.
We can build and embed a custom version of Text Zoom Readability Calculator for your brand and workflow.
Answers: is 125% zoom readable, ideal characters per line at 200% zoom, and effective font size after browser scaling.
Default 16px × 125% → 20px — compared to profile target (16/19/21 px).
Penalty 1.2 pts per character away from 70/60/55 target — default 72 chars scores 27.6.
Standard +5 at ≥110% zoom — default 125% qualifies.
Default: 16 px base · 125% zoom · 72 chars/line · standard → 20 px effective · score 44+27.6+5 = 76.6/100 · High.
Effective Size
20 px
Readability Score
76.6/100
Level
High
| Profile | Effective size | Line length | Zoom bonus |
|---|---|---|---|
| Standard | 16 px effective | ~70 | +5 if zoom ≥110% |
| Senior-friendly | 19 px effective | ~60 | +8 if zoom ≥125% |
| Low vision | 21 px effective | ~55 | +10 if zoom ≥150% |
| Component | Max | Formula | Default example |
|---|---|---|---|
| Size fit | 60 pts | 60 − |effective − target| × 4 | |20−16|×4 → 44 pts |
| Line length | 30 pts | 30 − |chars − target| × 1.2 | |72−70|×1.2 → 27.6 pts |
| Zoom bonus | 10 pts | Profile-dependent zoom thresholds | Standard 125% → +5 pts |
| Score | Level | Action |
|---|---|---|
| 0–39.9 | Low | Raise zoom and shorten line length toward profile targets |
| 40–69.9 | Moderate | Tune effective size ±2 px or line length ±5–10 chars |
| 70–100 | High | Validate contrast and reflow; maintain at 200% zoom test |
Typography planning heuristic for zoom and line length — validate reflow, contrast, and spacing separately for WCAG conformance.
effectivePx = baseFontPx × (zoom% ÷ 100)sizeScore = max(0, 60 − |effective − targetPx| × 4)lineScore = max(0, 30 − |chars − targetChars| × 1.2)score = min(100, sizeScore + lineScore + profileBonus)20 px effective · score 76.6 · High (not ~74 — verified 76.6).
16 px · score 92 · High — sizeScore 60, lineScore 30.
32 px effective · score 35 · Low — sizeScore 0 (far above 16px target); lineScore 30. WCAG 1.4.4 pass is separate — also test reflow and contrast at 200%.
22.5 px · score 79.2 · High.
28 px · score 72 · High (+10 zoom bonus).
9 px · score 14 · Low — needs ~150%+ zoom (21px target) and ~55-char lines; compare 16px×100% at 80 chars → 42 Moderate.
14 px · score 60 · Moderate.
10 px · score 38 · Low — increase base size or zoom.
Share with design systems teams, accessibility reviewers, and content designers testing browser zoom.
Suggested hashtags: #Accessibility #WCAG #Typography #Readability #InclusiveDesign