Octane Rating Converter — RON, AKI, MON
Convert between RON (Research Octane Number), AKI pump octane (USA), and MON (Motor Octane Number) ratings for gasoline and fuel comparisons.
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Gasoline octane ratings measure a fuel’s ability to resist “knocking” or pre-ignition inside an engine. The same fuel can have different numbers depending on which rating system is used — which causes confusion when traveling or comparing fuel grades internationally.
RON: Research Octane Number Used in Europe, Australia, Asia, and most of the world. Measured under low-speed, low-load engine conditions. Regular unleaded: 91–92 RON. Premium: 95–98 RON. Super premium: 100+ RON.
AKI: Anti-Knock Index (Pump Octane) Used in the United States and Canada. Shown on yellow stickers at fuel pumps as (R+M)/2. Formula: AKI = (RON + MON) / 2 Using the common approximation MON ≈ RON − 9: AKI ≈ RON − 4.5 Regular US gas: 87 AKI ≈ 91.5 RON. Premium: 91–93 AKI ≈ 95.5–97.5 RON.
MON: Motor Octane Number Measured under high-speed, high-load engine conditions. Always lower than RON — typically by about 8 to 10 points. MON ≈ RON − 9 (common approximation) Less visible to consumers but used in the AKI calculation.
Common fuel grade equivalents:
| Grade | RON | AKI (US) | MON |
|---|---|---|---|
| Regular (US) | 91 | 87 | 82 |
| Mid-grade (US) | 93 | 89 | 84 |
| Premium (US) | 96 | 91 | 87 |
| Super premium | 98 | 93.5 | 89 |
| E10 regular | 91 | 87 | 82 |
Note: These conversions use the standard approximation (MON = RON − 9). Actual MON values vary by fuel blend and season. Always follow your vehicle manufacturer’s recommendation.
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