What to wear in sweden in august-october?

Most people will wear jeans, T-shirts and if cold a sweater, over that will likely be a rainproof jacket. When it gets cold, October or later there will be a winter coat added. Heavy shoes are fine most of the time, if you are into hiking, proper waterproof hiking boots are a must, (although one guide in Norway, like climate, used waterproof boots, called wellingtons in England.) For city use, sport shoes will do till the snow starts falling. And in August you can even still get weather that is more suited to shorts. That 15 degrees is an average, there may be rare hot days too. If you live in a country that does not get that cold, think about getting your warm gear in Sweden, as the choice will be much wider and if you shop smart maybe even cheaper.  more