There are 3 Measures of Voter Turnouts:
 % of Registered Voters - RV
 % of Voting Age Population - VAP
 % of Voting Eligible Population - VEP (subtracting non-citizens and ineligible felons from the voting-age population and adding eligible overseas voters)
According to Pewresearch.org, compared to OECD countries:
On , VAP, the US does not compare well but 2016 was a comparatively good year
On , RV, the US fares better than most OECD countries
On , VEP, the US compares more favourably than on VAP
The US has one of the largest differences between VAP and RV
There is an interactive graph in the article below, with the comparison of VAP & RV for OECD countries.
The highest turnout rates
among OECD nations were in Belgium (87.2%), Sweden (82.6%) and Denmark (80.3%). Switzerland consistently has the lowest turnout
in the OECD: In 2015, less than 39% of the Swiss voting-age population cast ballots for the federal legislature.
One factor behind Belgium’s high turnout rates
– between 83% and 95% of VAP in every election for the past four decades – may be that it is one of the 24 nations around the world (and six in the OECD) with some form of compulsory voting
, according to IDEA. (One canton in Switzerland, also an OECD member nation, has compulsory voting.)
....... In many countries, the government takes the lead in getting people’s names on the rolls
– whether by registering them automatically once they become eligible (as in, for example, Sweden or Germany) or by aggressively seeking out and registering eligible voters (as in the UK and Australia). As a result, turnout looks pretty similar regardless of whether you’re looking at voting-age population or registered voters.In the U.S., by contrast, registration is mainly an individual responsibility.
......No matter how they’re measured, U.S. turnout rates have been fairly consistent over the past several decades, despite some election-to-election variation. Since 1976, voting-age turnout has remained within an 8.5-percentage-point range – from just under 50% in 1996, when Bill Clinton was re-elected, to just over 58% in 2008, when Barack Obama won the White House. However, turnout varies considerably among different racial, ethnic and age groups.