Measurement, time & conversions · Topic 15 of 15
Roman Numerals
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Math · Roman numerals
Roman Numerals
Seven symbols, I to M: a symbol after a larger or equal one adds; a smaller symbol placed before a larger one subtracts.
01 · The seven symbols1 I · 5 V · 10 X · 50 L · 100 C · 500 D · 1000 M
02 · The subtract ruleSmaller before larger = subtract
03 · The six pairsIV 4 · IX 9 · XL 40 · XC 90 · CD 400 · CM 900
01
The rules
Smaller or equal symbol after a larger one: add (XV = 15) must know
Smaller symbol before a larger one: subtract (IV = 4) must know
I, X, C, M repeat up to 3 times; V, L, D never repeat
Only I, X, C subtract — I from V/X, X from L/C, C from D/M
02
Know by heart
1 = I, 5 = V, 10 = X, 50 = L, 100 = C, 500 = D, 1,000 = M must know
The 6 subtractive pairs: IV 4, IX 9, XL 40, XC 90, CD 400, CM 900
03
Roman → Arabic
How to solve itRead left to right, comparing each symbol with the next
Smaller than the next? Subtract as a pair; otherwise add, then total
04
Arabic → Roman
How to solve itSplit by place value (1,000s, 100s, 10s, 1s), convert each, join
05
Worked examples
XLVII = 40 + 5 + 2 = 47
MDCCLXXVI = 1,000 + 500 + 200 + 50 + 20 + 6 = 1,776
349 = 300 + 40 + 9 = CCC XL IX = CCCXLIX
06
Add or subtract?
Commonly confused| Add | Subtract | |
|---|---|---|
| When | Symbol follows a larger or equal one | Smaller symbol sits before a larger one |
| Examples | VI = 6, XV = 15, LX = 60 | IV = 4, XL = 40, CM = 900 |
| Which symbols | Any symbol | Only I, X and C |
07
Common mistakes
49 = XLIX, not IL; 99 = XCIX, not IC
Never 4 in a row: 4 = IV (not IIII), 40 = XL (not XXXX)
08
More detail
Show 2 more facts
Clocks may show IIII for 4 — a custom, not the standard form
Standard numerals stop at 3,999 (MMMCMXCIX); a bar means × 1,000
Smaller after: add. Smaller before: subtract.
Sources · Math is Fun — Roman Numerals · Union Test Prep — HESI A2 Mathematics study guide, p. 5: Roman numerals · OpenExamPrep — HESI A2 Math 9.1: Roman numerals, additive and subtractive rules · Built from the verified NurseSavvy HESI A2 fact map (facts reviewed 2026-10-16). HESI is a trademark of Elsevier; NurseSavvy is not affiliated with Elsevier.
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