Luke Herbert Cataract and Retina Surgeon

Tool

Visual acuity converter

Sight can be written down in several ways: 6/12, 20/40, 70 letters, logMAR 0.30 and decimal 0.5 all describe the same vision. Type a value into any box to see it on the other scales.

Chart lines
Snellen US Snellen ETDRS letters logMAR Decimal
6/3 20/10 100 −0.30 2.0
6/3.8 20/12.5 95 −0.20 1.6
6/4.8 20/16 90 −0.10 1.25
6/5 20/17 89 −0.08 1.2
6/6 20/20 85 0.00 1.0
6/7.5 20/25 80 0.10 0.8
6/9 20/30 76 0.18 0.67
6/9.5 20/32 75 0.20 0.63
6/12 20/40 70 0.30 0.5
6/15 20/50 65 0.40 0.4
6/18 20/60 61 0.48 0.33
6/19 20/63 60 0.50 0.32
6/24 20/80 55 0.60 0.25
6/30 20/100 50 0.70 0.2
6/36 20/120 46 0.78 0.17
6/38 20/125 45 0.80 0.16
6/48 20/160 40 0.90 0.125
6/60 20/200 35 1.00 0.1
6/76 20/250 30 1.10 0.08
6/95 20/320 25 1.20 0.063
6/120 20/400 20 1.30 0.05
6/150 20/500 15 1.40 0.04
6/190 20/630 10 1.50 0.032
6/240 20/800 5 1.60 0.025
6/300 20/1000 0 1.70 0.02

6/5, 6/9, 6/18 and 6/36 are lines on traditional Snellen charts only. They fall between the lines of an ETDRS chart.

What the numbers mean

Snellen (6/12). The first number is the distance from the chart in metres, usually 6. The second is the distance at which someone with standard sight could read the smallest line you read. 6/6 is standard sight. 6/12 means you read at 6 metres what standard sight reads at 12. The bigger the second number, the poorer the sight. A traditional chart has only certain lines (6/60, 6/36, 6/24, 6/18, 6/12, 6/9, 6/6 and 6/5), so the converter also shows the likely line: the one you would most probably have been recorded at.

US Snellen (20/40). The same idea in feet. 20 feet is about 6 metres, so 20/20 is the same as 6/6. A traditional US chart has its own set of lines, from 20/200 down to 20/10, and the converter shows the likely one of those too.

ETDRS letters (70). The number of letters read correctly on an ETDRS chart, which many eye clinics and research studies use. Each line has five letters, and 85 letters is the same as 6/6. More letters means better sight.

logMAR (0.30). A scale used mainly in research. 0.00 is 6/6 and each line of an ETDRS chart is 0.1. Lower is better: a negative number is better than 6/6.

Decimal (0.5). Used in much of Europe. 1.0 is 6/6 and 0.5 is 6/12. Higher is better.

Sight worse than 6/60

The top letter of a Snellen chart is the 6/60 line. Measuring sight below that is harder, and it is done differently from clinic to clinic.

Some clinics move you closer to the chart and record the distance at which you can read the top letter. It may be checked at 3 metres and written as 3/60, or recorded wherever you first read it, such as 5/60, 2/60 or 1/60. These convert like any other Snellen result once scaled up to 6 metres: 3/60 is the same as 6/120, and 1/60 the same as 6/360.

Often, though, if you cannot read 6/60 the next step is to check whether you can:12

  • count fingers held up in front of you (CF), usually recorded with the distance, such as CF at 1 metre;
  • if not, see a hand moving (hand movements, HM);
  • if not, see a light (perception of light, PL), and whether you can tell which direction the light is coming from (with projection or without projection).

An eye that cannot see light at all is recorded as no perception of light (NPL).

Counting fingers, hand movements and perception of light are not points on a scale, so they have no true Snellen, letter or logMAR equivalent, and you cannot type them into the converter. For very poor sight, though, the likely line shows which of them a value most probably stands for, using the values research studies substitute for them.

Notes for clinicians

  • Every conversion goes through logMAR:
    • logMAR = log10(denominator ÷ numerator)
    • decimal = numerator ÷ denominator
    • letters = 85 − 50 × logMAR, the approximate ETDRS letter score of Gregori, Feuer and Rosenfeld3
  • A letter score converted from Snellen is an equivalent, not an ETDRS measurement. The same patient may score differently on an ETDRS chart.
  • Letter scores are rounded to the nearest letter. A result on a chart line is shown with the value printed on charts (6/9.5 rather than 6/9.51); anything else is shown to two significant figures.
  • The likely line is the line of a traditional chart nearest in logMAR: 6/60, 6/36, 6/24, 6/18, 6/12, 6/9, 6/6 and 6/5 in the UK; 20/200, 20/100, 20/70, 20/50, 20/40, 20/30, 20/25, 20/20, 20/15, 20/13 and 20/10 in the US. So 6/10 shows as 6/9, and 6/11 as 6/12. It is not shown for the box you typed in. More than half a letter worse than 6/60 (20/200), it shows the nearest of CF (logMAR 1.9), HM (2.3), PL (2.7) and NPL (3.0), the substitute values described below.
  • The letter score runs from 0 (6/300) to 100 (6/3). The converter accepts 6/3 to logMAR 3.0; Snellen and decimal values beyond about 6/600 are arithmetic, not chart measurements.
  • There is no valid conversion of CF, HM, PL or NPL to a letter score. Studies that need numbers for statistics substitute values instead, such as logMAR 1.9 to 2.0 for CF and 2.3 for HM, taken from measurements with the Freiburg Visual Acuity Test,45 and imputed values of 2.7 for PL and 3.0 for NPL;6 the values used differ between studies.7 Measured this way, CF lies beyond the bottom of the letter score, which reaches 0 letters at logMAR 1.7.

  1. Marsden J, Stevens S, Ebri A. How to measure distance visual acuity. Community Eye Health 2019;32(107):46. PMC7041831 ↩

  2. Tripathy K, Gupta A. Evaluation of visual acuity. In: StatPearls. StatPearls Publishing; updated 1 May 2024. NBK564307 ↩

  3. Gregori NZ, Feuer W, Rosenfeld PJ. Novel method for analyzing Snellen visual acuity measurements. Retina 2010;30(7):1046–50. doi:10.1097/IAE.0b013e3181d87e04 ↩

  4. Schulze-Bonsel K, Feltgen N, Burau H, Hansen L, Bach M. Visual acuities “hand motion” and “counting fingers” can be quantified with the Freiburg visual acuity test. Invest Ophthalmol Vis Sci 2006;47(3):1236–40. doi:10.1167/iovs.05-0981 ↩

  5. Lange C, Feltgen N, Junker B, Schulze-Bonsel K, Bach M. Resolving the clinical acuity categories “hand motion” and “counting fingers” using the Freiburg Visual Acuity Test (FrACT). Graefes Arch Clin Exp Ophthalmol 2009;247(1):137–42. doi:10.1007/s00417-008-0926-0 ↩

  6. Bach M. Visual acuity “cheat sheet” for high and low vision. michaelbach.de/sci/acuity.html, updated 30 July 2026. ↩

  7. Moussa G, Bassilious K, Mathews N. A novel excel sheet conversion tool from Snellen fraction to LogMAR including ‘counting fingers’, ‘hand movement’, ‘light perception’ and ‘no light perception’ and focused review of literature of low visual acuity reference values. Acta Ophthalmol 2021;99(6):e963–5. doi:10.1111/aos.14659 ↩

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