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/copper 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 the 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 quotes
siliqva
1/1728 (≈ 0.000579)
reversed curved E
scripvlvm
1/288 (≈ 0.00347)
reversed barred S
dimidia sextvla
1/144 (≈ 0.00694)
reversed S
sextvla
1/72 (≈ 0.01389)
reversed C
sicilicvs
1/48 (≈ 0.02083)
reversed SS
binae sextvlae
1/36 (≈ 0.02778)
curved E
semvncia
1/24 (≈ 0.04167)
dot
vncia
1/12 (≈ 0.083)
curved E plus dot
sesvncia
1/8 (= 0.125)
2 dots
sextans
1/6 (≈ 0.167)
3 dots
qvadrans
1/4 (= 0.25)
4 dots
triens
1/3 (≈ 0.3)
5 dots
qvincvnx
5/12 (≈ 0.4167)
S
semis
1/2 (= 0.5)
S plus dot
septvnx
7/12 (≈ 0.583)
S plus 2 dots
bes
2/3 (≈ 0.67)
S plus 3 dots
nonvncivm
3/4 (= 0.75)
S plus 4 dots
decvnx
5/6 (≈ 0.83)
S plus 5 dots
devnx
11/12 (≈ 0.9167)
I
as or vnvs
1
Enter fraction as numerator/denominator:
OR
Enter fraction as figures to right of decimal point: 0.
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.
Veni, vidi, dvci (I came, I saw, I calculated)