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Roman Fraction Converter

You’ll find any number of Roman numeral converters for whole numbers online — but really, just about anyone who made it past the fourth grade can manage that on their own.

Roman fractions, though, are another matter entirely. They were based on twelfths, or multiples or divisions of twelfths. The 1/12 fraction itself was vncia, from which we derive words like “inch” (1/12 of a foot) and “ounce” (1/12 of a troy pound). The word as for unity refers to a bronze coin of the Republic and Empire periods which likewise divided into various twelfths.

The chart shows the symbols most often cited1 and a verbal description, the Latin terms and how they typically would have appeared in manuscript at the time of Hadrian or thereabouts (many thanks to epigrapher Johan Winge for his enterprising alphabet reconstruction), and finally their modern equivalents. Below that are both slashed and decimal inputs for you to calculate any fraction down to a siliqva (1/1728, or 1/144 of an vncia).

right angle quotesright angle quotessiliqvasiliqua1/1728 (≈ 0.000579)
reversed curved Ereversed curved Escripvlvmscripulum1/288 (≈ 0.00347)
reversed barred Sreversed barred Sdimidia sextvladimidia sextula1/144 (≈ 0.00694)
reversed Sreversed Ssextvlasextula1/72 (≈ 0.01389)
reversed Creversed Csicilicvssicilicus1/48 (≈ 0.02083)
reversed SSreversed SSbinæ sextvlæbinae sextulae1/36 (≈ 0.02778)
curved Ecurved Esemvnciasemuncia1/24 (≈ 0.04167)
dotdotvnciauncia1/12 (≈ 0.083)
curved E plus dotcurved E plus dotsesvnciasesuncia1/8 (= 0.125)
2 dots2 dotssextanssextans1/6 (≈ 0.167)
3 dots3 dotsqvadransquadrans1/4 (= 0.25)
4 dots4 dotstrienstriens1/3 (≈ 0.3)
5 dots5 dotsqvincvnxquincunx5/12 (≈ 0.4167)
SSsemissemis1/2 (= 0.5)
S plus dotS plus dotseptvnxseptunx7/12 (≈ 0.583)
S plus 2 dotsS plus 2 dotsbesbes2/3 (≈ 0.67)
S plus 3 dotsS plus 3 dotsnonvncivmnonuncium3/4 (= 0.75)
S plus 4 dotsS plus 4 dotsdecvnxdecunx5/6 (≈ 0.83)
S plus 5 dotsS plus 5 dotsdevnxdeunx11/12 (≈ 0.9167)
IIas or vnvsas or unus1

Enter fraction as
OREnter fraction as figures
to right of decimal point:

And then we also have Latin DATE Conversions
“Chums, Italics, landsmen, heed my syllables...”
“I have a vewy gweat fwiend in Wome, his name is...”

asterisk  Veni, vidi, dvci (I came, I saw, I calculated)

1. Like Roman numerals, Roman fractional notation varied over time and also with the whims of those who employed it. Accordingly, you'll see symbols and terms that differ from what I show.

Nero bronze
vnvs coin of c. 66 ce photo courtesy of Classical Numismatic Group

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