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Visual Acuity Conversion Calculator

Work out visual acuity conversion instantly with clear inputs, formula shown and shareable results.

About Visual Acuity Conversion Calculator

Converts a Snellen fraction into logMAR and decimal acuity, and restates it in both imperial and metric notation.

Formula

Acuity conversion

logMAR = log10(denominator / reference distance); decimal acuity = reference / denominator; 20/20 = 6/6 = logMAR 0.00 = decimal 1.0

Worked example

With the default values below, Visual Acuity Conversion Calculator returns logMAR of 0.301. Change any input above and every figure here is recalculated in your browser.

Inputs used

Snellen denominatoraccepts 5–800
40
Notationone of Imperial 20 feet, Metric 6 metres
Imperial 20 feet

Results

logMAR
0.301
Decimal acuity
0.500
Imperial notation
20/40
Metric notation
6/12

Step by step

  1. 1Values used
  2. 2Acuity conversion
  3. 3logMAR= 0.301
  4. 4Decimal acuity= 0.500
  5. 5Imperial notation= 20/40
  6. 6Metric notation= 6/12

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Why do trials use logMAR?

logMAR steps are equal in size, so change can be averaged and analysed statistically, unlike Snellen fractions.

What logMAR counts as legal blindness?

Definitions vary, but 1.0 logMAR (6/60 or 20/200) is the common threshold in many jurisdictions.

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Visual Acuity Conversion Calculator | Calcrivo