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Calcimator

Visual Acuity Converter

Convert between Snellen fraction, LogMAR, decimal acuity, and MAR notation for visual acuity measurements.

Convert

Results

Decimal Acuity
1
LogMAR
0
MAR (Min Angle of Resolution)
1 arcmin
Metric Snellen (6/x)
6/6
How to Use This Calculator
  1. Enter the Snellen Numerator — the test distance in feet (typically 20 for US charts, 6 for metric).
  2. Enter the Snellen Denominator — the smallest line the patient reads (e.g., 20 for 20/20, 40 for 20/40).
  3. The calculator instantly converts to Decimal Acuity, LogMAR, MAR (Minimum Angle of Resolution), and the metric 6/x equivalent.
  4. LogMAR 0.0 = 20/20 (normal); positive LogMAR values indicate reduced acuity.
  5. Use these conversions when comparing results across clinical studies, visual acuity charts, or international records.

How the result changes with Snellen Denominator

Snellen DenominatorDecimal AcuityLogMAR
850.240.63
2830.071.15
5220.041.42
7210.031.56

What each input means

Snellen Numerator
Test distance in feet (typically 20 for US Snellen, 6 for metric).
Snellen Denominator
Smallest line read (e.g., 20 for 20/20, 40 for 20/40). Higher number = worse vision.

How this is calculated

Formula

LogMAR = log₁₀(denominator / numerator)

Worked example, using the default values

  1. Identify Input Parameters
    Snellen Numerator = 20, Snellen Denominator = 20 = 2 input(s) provided
  2. Calculate Decimal Acuity
    Decimal Acuity
    1 = 1
  3. Calculate LogMAR
    LogMAR
    0 = 0
  4. Calculate MAR
    MAR
    1 = 1
  5. Calculate Metric Snellen
    Metric Snellen
    6 = 6

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