πŸ”’ Roman to Decimal Converter

δΈ­ζ–‡ EN

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Updated: 2026-07-12

Roman to Decimal Converter

Enter a Roman numeral (such as IV, MCMXCIX) to instantly convert it to a decimal number. Supports case-insensitive input.

β†’
1994
MCMXCIV

Quick Input:

πŸ“– Conversion Method

Method: Read from left to right. If the current character value is less than the right character value, subtract the current value (e.g., IV=5-1=4). Otherwise, add the current value (e.g., VI=5+1=6).

Example: MCMXCIV = M(1000) + CM(900) + XC(90) + IV(4) = 1994

Valid characters: I(1), V(5), X(10), L(50), C(100), D(500), M(1000). Case-insensitive input supported.

❓ Frequently Asked Questions

Do I need to install any software?

No. Roman Numerals to Decimal is a web-based tool β€” just open it in your browser and start using it. No downloads, plugins, or extensions required.

Are there any usage limits for Roman Numerals to Decimal?

Roman Numerals to Decimal has no usage limits β€” it's free and unlimited. Since processing is done client-side, speed depends on your device. For very large files, we recommend processing in batches for the best experience.

Can I use Roman Numerals to Decimal on my phone?

Yes. Roman Numerals to Decimal is fully responsive and works on phones, tablets, and desktops. The interface adapts automatically to your screen size.

Is my data safe when using Roman Numerals to Decimal?

Absolutely. Everything runs locally: Roman Numeral and other values are processed on your device, never sent to a server. No data is sent to any server, so there's zero risk of data leaks. Your information stays completely under your control.

Are converted files compatible with other software?

Yes. Converted files follow standard format specifications and are compatible with mainstream software and platforms.

// === Roman Numeral to Decimal Implementation === var ROMAN_MAP = {I:1, V:5, X:10, L:50, C:100, D:500, M:1000}; // Validate and convert Roman numeral -> decimal, returns null if invalid function romanToDecimal(s) { if (!s) return null; var str = s.trim().toUpperCase(); if (!str) return null; var total = 0; var prev = 0; for (var i = 0; i < str.length; i++) { var c = str.charAt(i); if (!ROMAN_MAP.hasOwnProperty(c)) return null; var v = ROMAN_MAP[c]; if (v > prev) { // Subtractive combination (e.g. IV: add 1 then subtract 1*2) total += v - 2 * prev; } else { total += v; } prev = v; } if (total < 1 || total > 3999) return null; return total; } function convert() { var input = document.getElementById('romanInput').value; var errEl = document.getElementById('errorMsg'); var outEl = document.getElementById('decimalOutput'); var echoEl = document.getElementById('romanEcho'); if (!input.trim()) { errEl.textContent = 'Please enter a Roman numeral'; outEl.textContent = '--'; echoEl.textContent = ''; return; } var n = romanToDecimal(input); if (n === null) { errEl.textContent = 'Invalid Roman numeral. Only I V X L C D M are supported (range 1-3999)'; outEl.textContent = '--'; echoEl.textContent = ''; return; } errEl.textContent = ''; outEl.textContent = String(n); echoEl.textContent = input.trim().toUpperCase(); } function copyDecimal() { var outEl = document.getElementById('decimalOutput'); if (!outEl || outEl.textContent === '--' || outEl.textContent === '') { showToast('Nothing to copy'); return; } var t = outEl.textContent; navigator.clipboard.writeText(t).then(function(){showToast('Copied')})['catch'](function(){showToast('Copy failed')}); } function setRoman(v) { document.getElementById('romanInput').value = v; convert(); } // Run once on page load convert(); function showToast(msg) { var t = document.getElementById('toast'); if (!t) return; t.textContent = msg; t.classList.add('show'); setTimeout(function(){ t.classList.remove('show'); }, 2000); }