Visual Acuity Chart Generator - Snellen, Tumbling E & Landolt C
Generate professional, printable eye charts (Snellen, Tumbling E, Landolt C) calibrated to your screen or viewing distance. Standard medical formulas included.
About
This tool generates clinically accurate Visual Acuity Charts based on standard optometric formulas. Unlike static images, this generator calibrates to your specific screen resolution or print size, ensuring that the optotypes (letters) subtend exactly 5 minutes of arc at your chosen viewing distance.
Accurate vision testing requires precise geometry. A standard 20/20 letter must occupy a vertical visual angle of 5' (arcminutes), with each stroke thickness occupying 1'. This tool handles the trigonometry to scale standard Sloan letters, Tumbling E's, or Landolt C's to the correct pixel or millimeter height for your environment.
Formulas
The height of an optotype h is determined by the viewing distance d and the visual angle θ. For a standard 20/20 letter, θ is 5 minutes of arc.
Since θ is small, we can approximate:
Where:
- h = Letter height (mm)
- d = Viewing distance (mm)
- tan = Tangent function
Reference Data
| Snellen (ft) | Metric (m) | LogMAR | Visual Angle (min) | Letter Height at 6m (mm) |
|---|---|---|---|---|
| 20/200 | 6/60 | 1.0 | 50' | 87.26 |
| 20/100 | 6/30 | 0.7 | 25' | 43.63 |
| 20/70 | 6/21 | 0.54 | 17.5' | 30.54 |
| 20/50 | 6/15 | 0.4 | 12.5' | 21.82 |
| 20/40 | 6/12 | 0.3 | 10' | 17.45 |
| 20/30 | 6/9 | 0.18 | 7.5' | 13.09 |
| 20/20 | 6/6 | 0.0 | 5' | 8.73 |
| 20/15 | 6/4.5 | -0.12 | 3.75' | 6.54 |
| 20/10 | 6/3 | -0.3 | 2.5' | 4.36 |