When asked what proportion of the country's population was Muslim, the average guess was 17 percent. In reality, around 460,000 Muslims live in Sweden, or 4.6 percent of the total population.
That makes them the fifth worst out of the EU countries polled – and in 11th place if non-Europeans are included – at guessing the Muslim population, with France, Italy, Germany and Belgium being the only other EU member states with a wider so-called 'perception gap'.
Islam is Sweden's second largest religion after Christianity. Around 27 percent are not affiliated with any religion, according to the Pew Research Centre.
Graph 1: What percentage of your country do you think is Muslim?
The figures come from Ipsos Mori Perils of Perception 2016, which surved approximately 500 Swedish adults as well as people in 40 countries around the world.
It also asked what they thought the Muslim proportion of the population would be in 2020.
Again, Swedes drastically overestimated the numbers, predicting that more than a quarter of the country (27 percent) would be Muslim within four years, whereas the actual projected figure – based on data from the Pew Research Centre – is 6.5 percent.
Graph 2: What do you think the Muslim population will be in 2020?
The survey also asked questions about things like overall population, wealth, home ownership and happiness.
Asked how many of Sweden's citizens had told the World Values Survey they were happy, Swedes answered less than half. In fact, 95 percent of respondents had described themselves as happy.
Bobby Duffy, managing director of Ipsos Public Affairs, said it was a widespread trend that people "overestimated what they worried about".
"We are often more incorrect on factors that are widely discussed in the media, such as the proportion of our population that are Muslims and wealth inequality," he said in a statement.
Overall, Swedens performed better than most other countries in Ipsos' Index of Ignorance, which ranked countries in terms of how far from reality their responses were. In compiling this index, only the questions based on reality (and not projections) were taken into account.
Swedes placed 31st out of 40 in the index, meaning only nine countries performed better. The Netherlands were the most accurate in their estimates, and India the least accurate.