Example:

Roman numerals are also still used on objects that indicate time (i.e., watches, clocks).

In the Arabic system, numbers, not letters, are used to express amounts. The Arabic system also uses fractions (½) and decimals (0.5).

Most medication dosages are ordered using metric measurements and Arabic numbers; however, on rare occasions medication orders may include a Roman numeral.

Example:

Aspirin gr x, which is correctly interpreted as aspirin 10 grains

To calculate drug dosages and assist in the prevention of medication errors, nurses need to know both Roman numerals and Arabic numbers. Lowercase letters are usually used to express Roman numerals in relation to medications. The Roman numerals you will see most often in the calculation of dosages are built on the basic symbols i, v, and x. To prevent errors in interpretation a line is sometimes drawn over the symbol. If this line is used, the lowercase “i” is dotted above the line, not below.

Example 1:

10 grains = gr x

Example 2:

2 = ii¯

When the symbol for ½ (ss) is used in conjunction with Roman numerals, the symbol is placed at the end.

Example 1:

312=iii¯ss=iiiss¯

Example 2:

112grains=gr i¯ss=gr iss¯

Box 1-1 lists the common Arabic equivalents for Roman numerals (review them if necessary). They are often expressed with lowercase letters. Review this list before proceeding to the rules pertaining to Roman numerals as shown on p. 6. You will most commonly see Roman numerals up to the value of 30 when they are used in relation to medications.

BOX 1-1   Arabic Equivalents for Roman Numerals

Arabic Number	Roman Numeral
½	ss or ss
1	i or i, I
2	ii or ii, II
3	iii or iii, III
4	iv or iv, IV
5	v or v, V
6	vi or vi, VI
7	vii or vii, VII
8	viii or viii, VIII
9	ix or ix, IX
10	x or x, X
15	xv or xv, XV
20	xx or xx, XX
30	xxx or xxx, XXX

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