{lang: 'en'} Roman numerals

 Individual digits: I = 1 V = 5 X = 10 L = 50 C = 100 D = 500 M = 1000 Add repeated digits, and lesserdigits positioned after greater: III = 3 VI = 6 VII = 7 VIII = 8 XI = 11 XV = 15 XVI = 16 XX = 20 CXII = 112
 Subtract lesser digitspositioned before greater: IV = 4 IX = 9 XL = 40 XLIX = 49* XC = 90 XCIX = 99* CM = 900 At most three repeats**, at mostone lesser digit in front of greater: III = 3 IV = 4** VIII = 8 IX = 9 XIII = 13 XIV = 14 XVIII = 18 XIX = 19 1-25: I = 1 II = 2 III = 3 IV = 4 V = 5 VI = 6 VII = 7 VIII = 8 IX = 9 X = 10 XI = 11 XII = 12 XIII = 13 XIV = 14 XV = 15 XVI = 16 XVII = 17 XVIII = 18 XIX = 19 XX = 20 XXI = 21 XXII = 22 XXIII = 23 XXIV = 24 XXV = 25
 Examples of larger numbers: MCMLVII = 1957 MCMLXXXVIII = 1988 MCMXCI = 1991 MCMXCIX = 1999* MM = 2000 MMI = 2001 MMXLVI = 2046 MMCXXIV = 2124 MMDCCXLVII = 2747 * Lesser digit in front of greater: at most two digits difference, 99 = XCIX (and not IC), 990 = CMXC (and not XM), 1999 = MCMXCIX (and not MIM).
** At most tree repetitions: V, L and D are never repeated. According to older roman principle the digit I can sometimes be repeated more than tree times, for example 4 = IIII on some clocks. M can always be repeated more than three times.

To write very large numbers an extra horisontal line above the digits can be used, multiplying their values by 1000.

 This is an English language version of a page at faktabanken.nu. The corresponding Swedish language page is here.