How Small Can Text Be Before OCR Fails? A Measurement

Result

What the numbers say

• Perfect accuracy arrives at 9–14 pixels of cap height, depending on the typeface — not 30–40. Every sample at or above that height came back character-for-character identical.
• The collapse is sudden and it happens at 4–6 pixels. Arial holds 95.8% at a 6px cap and drops to 0% at 4px. There is no gentle decline: two pixels separate "mostly right" from "nothing usable".
• Monospace tolerates the smallest sizes. Courier New was still at 99.2% with a 6px cap, where Georgia managed 98.8% at 7px and needed 14px to be perfect. Uniform advance width and open counters survive downsampling better than a serif with fine strokes.
• Between 7px and 12px the errors are single characters, typically a comma read as a full stop or a merged space. Accuracy sits at 99%+ but exact-match does not, which matters if you are parsing rather than reading.

Method

• Engine: Tesseract.js 5 (WebAssembly), eng.traineddata — the same build the site's OCR tool runs.
• Metric: Character error rate — Levenshtein distance over ground-truth length, whitespace normalised.
• Rendering: HTML5 Canvas, pure black on pure white, no noise, no skew, no compression.
• Cap height is the measured ink height of a capital H at each size, not the CSS font-size. Cap height is roughly 0.7em but varies by typeface: at 6px, Arial renders a 4px cap and Courier New renders 1px.
• Runs: 33 size-and-font combinations × 5 samples = 165 recognitions.
• Date: 2026-07-29.

The harness is in the repository at scripts/ocr-benchmark.mjs and needs only Playwright to re-run. Differences of a few tenths of a percent between adjacent sizes are run-to-run noise, not signal — Courier New reading 99.58% at a 14px cap and 100% at 9px is the clearest example.

The five sample strings

Chosen to include the things OCR actually struggles with — digits next to letters, punctuation, mixed case, an email address and a reference code — rather than clean prose alone.

• The quick brown fox jumps over the lazy dog
• Invoice 4820 total 173,880 VAT 8% due 29 July
• Contact: hello@example.com or +84 90 123 4567
• Mixed CASE with punctuation; colons, dashes - and (brackets)
• Order #A7-2291 shipped 03/11/2026 weight 1.45kg

Full results