I bought my Ford EcoSport (2019) a few days ago.

The dealership put £20 worth of fuel in it.

After some time of owning it, each time I started the engine, it correctly started telling me I had limited fuel remaining (26 miles left, 22 miles left etc).

I know the car has a 53l tank and, when the car told me I had an estimated 22 miles remaining, I filled it until the pump 'clicked'. 43.7l had been in it.

That means that, even though the car was telling it was quite lot, it had 9.3l of the 53l in the tank!

I know all cars play it safe but my question is: If I turn the car on when it's at, say, "1 mile left", I presume it still has at least another 30+ miles remaining in reality?

Most likely you will get another 30+ miles but do you really want to play that lottery? 

It's generally about 5L left when it says 0 miles on most modern cars (or Fords at least)

It's not good to run it right out though.

Also my mum had issues before where she kept only topping up £5-10 here and there then the fuel gauge got stuck. Mechanical told her to fill it up every now and then so it can measure from top, keep itself calibrated.

One of my Mondeos, I switched it on one day to go and play golf (as you do when you have a Mondeo) and it told me I had 30 miles left. 

Got just near the golf club and it started coughing. Looked down and it was saying 0 miles. I had only driven about 6.

Then conked out as I tried to get to the nearest petrol station and destroyed the fuel pump from running empty. 

Point is...the thing lies. Don't take the chance!

Cheers, lads.

My point was that I had 9l left of the 53l tank.

Considering it's telling me there are zero miles left, 17% of the tank remaining is quite a lot!

It should also be noted that Ford's own literature can be wrong for the stated capacity.

It says my ST is 42L in the brochure although I've put more than that in with miles still to go. The manual says something like 46 or 48 iirc.

On your first post you said you had 22 miles left showing then filled up, now you saying zero? 

What fuel economy figure does it show? 

When showing zero you should have approx 5 litres in the tank , and that is deliberately done so you don't run out. 

The fuel gauge is a gauge, just that . Not accurate to the last mile or litre. The remaining miles is an approximate value based on the approximate fuel level and the previous fuel economy over the last few miles( my guess is the last couple of journeys in my car. ) So you can in practice start the day on for instance say 50 miles remaining, then drive 10 miles very economicaly and still have 50 miles remaining or even increase. 

On my Mondeo on full tank  I can have 650 miles remaining, drive 90 miles economically on motorway and then have 680 remaining for my return journey.