Once you get past 20 or so, converting Roman numerals to Arabic (or vice versa) can be tricky. But you can save time and improve accuracy with a pair of Excel functions.

To convert an Arabic number to its classic Roman numeral, use:

**=ROMAN(A1)**

Naturally, you can place a number directly into the parentheses or choose any cell in your worksheet to reference - as long as the value is between 1 and 3999.

Turning Roman numbers into Arabic is slightly trickier, but still pretty simple. Paste in this formula:

**=MATCH(A1,ROMAN(ROW(INDIRECT("1:3999"))),0)**

But don't hit **Enter**. Instead, use **Ctrl-Shift-Enter**. This makes it an array formula, which should handily make the conversion as long as your Roman numeral value is in the same 1 to 3999 range.

Here are some examples of these functions in action:

Suzanne

Doesn't seem to work in openofffice Calc, probably because this sense of INDIRECT() is an undocumented dingus in Excel.