Presuming you’re based in the UK, I think you can expect the following averages from a ForTwo:
Peak of summer: 92 miles
Spring/autumn: 74 miles
Peak of winter: 61 miles
Of course there are all sort of factors, though. The figures above are if you always use ECO mode without heating or air-conditioning. Expect those figures to drop by at least 8 miles when you use the heater (to blow warm air) or use air-conditioning. Blowing cold air doesn’t affect the car’s range. Keeping the temperature at 20c when using AC and 22 when using the heater make quite a difference and improve your range. Try using AC at 18c and you’ll see what I mean…
And your average speed will make a difference; as will air temperature, rain, etc. Those are the figures I get and I drive an average of 66mph during the summer and 53mph during the winter over a daily round trip of roughly 77 miles/116km. (those speeds and ranges are converted from kilometres).
I just finished tracking my full charges over a period of a year: https://docs.google.com/spreadsheets/d/1Am9b8N6VhG5JximgODYYCQ8v7xWu3CDvWY65_Gn95Gk/edit#gid=0 And you can see more about my experience over the past year here: https://www.youtube.com/channel/UCH_PwIAtEe4xGZ_Y9ucZdBg?view_as=subscriber
And if you’re going to buy one, buy the optional 22kW charger - it’ll be money worth spent!