Roman Numeral Calculator
Two modes — pick your style and do maths the Roman way!
Roman Keypad
Type using Roman symbols. Invalid combinations are flagged instantly as you build your numeral.
Number Keypad
Enter regular numbers. Every number — including the result — is shown as a Roman numeral.
How It Works
Choose your input mode
Pick Roman Keypad to type directly with Roman symbols (M, D, C, L, X, V, I), or switch to Number Keypad to enter regular numbers — the calculator converts everything for you automatically.
Enter your numbers and choose an operation
Tap your first number, then press an operator — + (add), − (subtract), × (multiply), or ÷ (divide). Then enter your second number. A live hint strip validates your Roman numeral as you type and shows its decimal value.
Press = to see the result as a Roman numeral
Hit the = button and the answer appears in Roman numerals alongside a step-by-step breakdown. Results must fall between 1 and 3,999 — the standard range for Roman numerals. For background on the symbols, visit the Roman numerals chart →
Example Calculations
| Expression | In Roman Numerals | Result |
|---|---|---|
| 10 + 5 = 15 | X + V | XV |
| 50 − 10 = 40 | L − X | XL |
| 5 × 4 = 20 | V × IV | XX |
| 10 ÷ 2 = 5 | X ÷ II | V |
| 100 + 400 = 500 | C + CD | D |
| 1000 × 3 = 3000 | M × III | MMM |
Need to look up any of these symbols? Check our full Roman numerals chart →
Frequently Asked Questions
Can you actually do arithmetic with Roman numerals?
Yes — but it's surprisingly tricky! Unlike our place-value system, Roman numerals have no positional logic, which makes carrying and borrowing awkward. That's exactly why ancient Romans relied heavily on the abacus for real calculations and used Roman numerals mainly for recording results. This calculator does the hard work for you — just tap and go.
What operations does the calculator support?
The calculator supports all four basic operations: addition (+), subtraction (−), multiplication (×), and division (÷). Division uses whole-number (integer) results — any remainder is shown in the step-by-step breakdown, since Roman numerals can't represent fractions or decimals. To understand the symbols used in results, visit our Roman numeral rules page →
What happens if the result is 0 or negative?
Roman numerals simply cannot express zero or negative numbers — the system was invented purely for counting positive quantities. If your calculation produces a result of 0 or less, the calculator will display the decimal answer but note it's outside the Roman numeral range. Curious why zero is so special? Read our dedicated zero in Roman numerals → page.
What's the largest calculation I can do?
Both inputs must be between 1 and 3,999 — the standard range of Roman numerals (I to MMMCMXCIX). The result also needs to fall within that range to be expressible as a Roman numeral. For numbers beyond 3,999 and how historians handled them, see our large Roman numbers guide →
Did Romans actually use Roman numerals for maths?
Not really! Roman numerals were primarily a writing and record-keeping system — merchants, scribes, and officials used them to label quantities, dates, and lists. For actual arithmetic, Romans used the calculi (counting stones) and hand-held abacus boards. The numeral system was so awkward for calculation that the adoption of Hindu-Arabic numerals (0–9) in medieval Europe was considered a major intellectual breakthrough. Test your knowledge with our Roman numerals quiz →