Cicero to Millimeter Converter

How it is calculated

The tool uses one fixed factor, 1 cicero = 4.5113 mm, and the Didot relation 1 cicero = 12 Didot points. Cicero to millimetre: mm = cicero × 4.5113. Millimetre to cicero: cicero = mm ÷ 4.5113. In both directions it also reports the length in Didot points (points = cicero × 12). Millimetre and cicero results are shown to four decimals, points to two. A negative or empty value returns no result, zero is accepted and gives zero, and any direction other than millimetre-to-cicero is treated as cicero-to-millimetre. The factor is the Didot one, not the Anglo-American pica.

Common mistakes

• Using the Anglo-American pica (about 4.2175 mm) or a 72.27-per-inch point for a Didot specification. The two systems differ by roughly 7%, which adds up quickly over a full page.
• Leaving the direction on cicero-to-millimetre when the number you have is already in millimetres, so the result is about 4.5 times too large.
• Confusing ciceros with Didot points: 12 points make one cicero, so a 10 point type size is not 10 ciceros.
• Rounding the factor to 4.5 mm; on a 42 cicero column that already shifts the width by about half a millimetre.
• Entering a negative value to mean an offset or overhang. The tool only accepts zero or positive lengths and shows no result otherwise.