ETDRS letters to Snellen (feet)
Type a value in letters to get it in Snellen (ft) instantly.
20/399Snellen (ft)
Nothing on our list is smaller: the US legal blindness limit (20/200) is 2× sharper. What a normal eye reads at 20 ft (6 m), this eye reads from about 1.002 ft (0.3007 m).
Convert the other way: Snellen (ft) to letters
What it means
How sharp is that?
For information only: an eye test also depends on the chart, lighting and the examiner. Ask an optometrist about your own eyes.
The math
How to convert letters to Snellen (ft)
Decimal = 20 ÷ x for 20/x, or 6 ÷ x for 6/x; logMAR = −log₁₀(decimal); ETDRS letters = 85 − 50 × logMAR.
Example: 20 letters = 20/399 Snellen (ft).
Every unit
That eyesight in every notation
Tables
letters to Snellen (ft) conversion table
| letters | Snellen (ft) |
|---|---|
| 19.9 letters | 20/401 Snellen (ft) |
| 35 letters | 20/200 Snellen (ft) |
| 50.1 letters | 20/100 Snellen (ft) |
| 54.9 letters | 20/80 Snellen (ft) |
| 57.8 letters | 20/70 Snellen (ft) |
| 61.1 letters | 20/60 Snellen (ft) |
| 65.1 letters | 20/50 Snellen (ft) |
| 69.9 letters | 20/40 Snellen (ft) |
| 76.2 letters | 20/30 Snellen (ft) |
| 80.2 letters | 20/25 Snellen (ft) |
| 85 letters | 20/20 Snellen (ft) |
| 91.2 letters | 20/15 Snellen (ft) |
| 100 letters | 20/10 Snellen (ft) |
Snellen (ft) to letters conversion table
| Snellen (ft) | letters |
|---|---|
| 20/10 Snellen (ft) | 100.051 letters |
| 20/15 Snellen (ft) | 91.2469 letters |
| 20/20 Snellen (ft) | 85 letters |
| 20/25 Snellen (ft) | 80.1545 letters |
| 20/30 Snellen (ft) | 76.1954 letters |
| 20/40 Snellen (ft) | 69.9485 letters |
| 20/50 Snellen (ft) | 65.103 letters |
| 20/60 Snellen (ft) | 61.1439 letters |
| 20/70 Snellen (ft) | 57.7966 letters |
| 20/80 Snellen (ft) | 54.897 letters |
| 20/100 Snellen (ft) | 50.0515 letters |
| 20/200 Snellen (ft) | 35 letters |
| 20/400 Snellen (ft) | 19.9485 letters |
Quick answers
Quick answers
- How many Snellen (ft) is 1 letters?
- 1 letters is 20/957 Snellen (ft).
- How many Snellen (ft) is 10 letters?
- 10 letters is 20/632 Snellen (ft).
- How many Snellen (ft) is 20 letters?
- 20 letters is 20/399 Snellen (ft).
The units
About these units
ETDRS letters (letters)
Letters read on an ETDRS chart: 85 at logMAR 0, 5 per line.
Snellen (feet) (Snellen (ft))
The US fraction: 20 feet over the normal distance.
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