Visual Acuity Converter (Snellen / logMAR / decimal)
Convert between Snellen (20-foot and 6-meter), decimal, and logMAR visual-acuity notations.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Notation entered
- Snellen imperial (20/x)
- Value
- 40
Result: Snellen 20/40 (6/12) = decimal 0.5 = logMAR 0.3.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Low vision
- Count-fingers, hand-motion, and light-perception are non-numeric categories below chart acuity and are not converted to a Snellen fraction.
What you enter
- Notation entered
- Value (Snellen denominator / decimal / logMAR)
How this is calculated
- Formula
- logMAR = log10(Snellen denominator/20) = −log10(decimal); decimal = 20/denominator. 20/20 = decimal 1.0 = logMAR 0.
Holladay JT. Visual acuity measurements. J Cataract Refract Surg. 2004;30(2):287-290. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.