I know a lot of people measure their fuel efficiency by "how far do I usually go on a tank".

But if you really want to know your mileage (and compare with others), you need a bit more accuracy.

You can't trust the trip computer! They're can be off by a few percent up to 10%. (Hopefully if enough people report, we can figure out where the Micra's gauge falls in the range.)

Here's what to do:

1) Next time you get gas, *fill* the tank. You can't calculate mileage if you're in the habit of just adding $10 or $20 worth each time. So fill until the pump clicks off once or twice.

2) Reset your trip odometer. If you don't have one (the Micra does), write down your current odometer reading.

3) Drive, drive, drive!

4) Next time you need fuel: again, completely fill the tank until the pump stops. GET THE RECEIPT.

5) On the receipt, write the distance from your trip odo (or regular odometer) you went since the previous fill up.

6) To get L/100 km, divide amount of fuel used (in L) by the distance driven and multiply by 100. That's your fuel economy.

E.G. let's say you went 595 km and you refilled the tank by adding 34.9 litres. 34.9 L / 595 km * 100 = 5.9 L/100 km.

7) Keep doing this each time you get gas. Save your receipts/calculations in your glove box or wherever. After a few fill-ups you'll be able to see what's "normal" for your car (assuming you do the same type of driving for each tank), and you can start using this info as a baseline from which you can try to improve.

I'd also record what the computer says you got (e.g. "5.6 L/100km") so you can start to get an idea of how optimistic the onboard gauge is.