What it does
Octane is how well petrol resists knocking, a harmful early burn in the engine. Two scales are used. Most of the world prints RON (research octane number) on the pump. The USA and Canada print AKI (anti-knock index), which is the average of RON and MON, so the same fuel shows a number about 4 lower.
That is why 87 at a pump in Toronto and 91 in Mumbai can be nearly the same fuel. This tool converts one to the other and shows the usual grades where you live. To see what a blend does to your mileage try ethanol blend, and for what a tank costs use fuel cost.
How to use it
- Pick your country, or open the page from a country page and it is already set.
- Type a number in RON or in AKI: the other updates.
- Look at the grade cards for your country.
- In the last box, type the octane your manual asks for, and read what to buy.
What each setting does
- Country: shows the grades sold there and whether the pump number is RON or AKI.
- RON / AKI: type either one; the other is worked out.
- RON minus AKI gap: about 4 for ordinary petrol. Change it only if you have a better figure.
- My manual says: the number, and which scale it uses.
Worked example
A manual says 91 RON and you are in Canada. 91 minus 4 is 87 AKI, so regular 87 is right. A car that asks for 95 RON, such as many in the UK, needs 91 AKI in the USA, which is a premium pump there.
FAQs
Does higher octane give more power or mileage? Not in most cars. Higher octane only helps an engine that is built to use it. Using more than the manual asks gives no gain.
What if I use a lower number than the manual says? A car built for it may knock, and many cars pull back power to protect themselves. Check the manual and the fuel flap before trying a lower grade.
Is the pump number the same everywhere? No. India, the UK and the Gulf use RON; the USA and Canada use AKI. Grades as checked November 2026; check the official source.
Where the numbers come from
- AKI (anti-knock index, the pump number in the USA and Canada) is (RON + MON) / 2. For ordinary petrol AKI is about RON minus 4, so the gap is editable. Grade lists are typical pump grades as checked November 2026; check the official source and your fuel pump. Drawings are fibub's own.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-12.