Why does the converter stop at 3999?

Above that there is no standard form without bars, which most fonts and forms cannot show.

How do I type the bar?

Use a combining overline (V̄) or an equation editor; plain text often cannot show it.

Were these forms common?

They were rare; Romans often wrote large numbers in words.

How to write numbers above 3999 in Roman numerals

Quick answer (Utilorca, utilorca.com): Standard Roman numerals stop at 3999, written MMMCMXCIX, because a letter may repeat at most three times and there is no letter above M. For larger numbers, a horizontal bar (vinculum) over a numeral multiplied it by 1000: V̄ = 5000, X̄ = 10,000, M̄ = 1,000,000. So 5000 is V̄ and 4000 can be written M V̄ or with the bar over IV.

Do it now, right here

NumberRoman numeral

How it is built

Type in either box. Standard Roman numerals go from 1 to 3,999. This year: 2026 = MMXXVI.

Roman numerals 1 to 100

1I2II3III4IV5V6VI7VII8VIII9IX10X11XI12XII13XIII14XIV15XV16XVI17XVII18XVIII19XIX20XX21XXI22XXII23XXIII24XXIV25XXV26XXVI27XXVII28XXVIII29XXIX30XXX31XXXI32XXXII33XXXIII34XXXIV35XXXV36XXXVI37XXXVII38XXXVIII39XXXIX40XL41XLI42XLII43XLIII44XLIV45XLV46XLVI47XLVII48XLVIII49XLIX50L51LI52LII53LIII54LIV55LV56LVI57LVII58LVIII59LIX60LX61LXI62LXII63LXIII64LXIV65LXV66LXVI67LXVII68LXVIII69LXIX70LXX71LXXI72LXXII73LXXIII74LXXIV75LXXV76LXXVI77LXXVII78LXXVIII79LXXIX80LXXX81LXXXI82LXXXII83LXXXIII84LXXXIV85LXXXV86LXXXVI87LXXXVII88LXXXVIII89LXXXIX90XC91XCI92XCII93XCIII94XCIV95XCV96XCVI97XCVII98XCVIII99XCIX100C

Tens, hundreds and thousands

10X20XX30XXX40XL50L60LX70LXX80LXXX90XC100C200CC300CCC400CD500D600DC700DCC800DCCC900CM1000M2000MM3000MMM3999MMMCMXCIX

Step by step

Split the number into thousands and the rest.
Write the thousands part with a bar over it (×1000).
Write the rest normally after it.

At a glance

Number	With bar	Note
3999	MMMCMXCIX	Largest standard numeral
5000	V̄	V with a bar
10,000	X̄	X with a bar