What is the difference between RON, MON and AKI?

RON (Research Octane Number) is measured under mild test conditions and is the figure shown on European and most Asian pumps. MON (Motor Octane Number) uses harsher conditions and is a few points lower. AKI (Anti-Knock Index), shown in the US and Canada, is the average of the two: (RON + MON) / 2.

Why is US 87 the same as European 91-92?

Because the US displays AKI (the RON/MON average) while Europe displays RON. US regular at 87 AKI is roughly 91-92 RON, mid-grade 89 AKI ≈ 93-94 RON, and premium 91-93 AKI ≈ 95-98 RON. The fuel is comparable; only the displayed scale differs.

Does higher octane give more power?

Only if your engine needs it. Octane measures resistance to knock (pre-ignition), not energy content. Engines tuned for high octane make more power and efficiency on it; in a low-compression engine, premium fuel gives no benefit. Always meet, but rarely exceed, the manufacturer's minimum.

What happens if I use lower octane than required?

The engine may knock — uncontrolled detonation that can damage pistons and valves. Modern engines retard ignition timing to prevent knock, which reduces power and economy. Persistently under-fuelling a high-compression engine risks long-term damage, so meet the specified minimum.

Is this conversion done online?

No. The octane scale conversion and country data run entirely in your browser. Nothing is sent anywhere.

Fuel Octane Rating Reference

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Petrol octane ratings

Octane rating measures a fuel’s resistance to knock — the higher the number, the more the fuel resists pre-ignition under compression. But three different scales exist, and a country’s pump number depends on which it displays. This reference compares RON, MON and AKI, converts between them, and lists what each grade means by country.

How it works

The same fuel is tested two ways. RON uses mild conditions; MON uses harsher, higher-load conditions and reads several points lower. Europe, the UK, Australia and most of Asia display RON. The US and Canada display AKI, the Anti-Knock Index, defined as AKI = (RON + MON) / 2. The gap between RON and MON (the “sensitivity”) is typically 8-10 points for pump petrol, so a fair estimate is MON ≈ RON − 9 and therefore AKI ≈ RON − 4.5. The converter applies these relationships so you can translate any pump number to the others.

Tips and examples

When travelling, don’t be alarmed that US “87” looks lower than European “95” — they are close: 87 AKI ≈ 91-92 RON. Match your engine’s minimum: a car needing 95 RON in Europe needs roughly 91 AKI premium in the US. Higher octane carries no more energy, so paying for premium in an engine that doesn’t require it wastes money. Conversely, under-fuelling a high-compression or turbo engine causes knock, lost power and possible damage. The conversion here uses a typical sensitivity and is an estimate — exact MON varies by blend.