Europe's comparatively high tax burden has created big marginal effects and tax wedges. For example a 2007 report by a right-wing thinktank, Timbro, calculated the amount going to the service worker's wallet is approximately 10% in Belgium, 15% in Sweden, 30% in Ireland and the UK, compared to 50% in the United States.
These are not the standard calculations of tax wedges as measured internationally, as well as being over a decade out of date.
A better source might be the OECD's publication Taxing Wages. The 2016 report (page 19) includes the following numbers for tax wedges as a % of labour costs in 2015 for a single person (no family) on average wages:
Total tax wedge Income tax Social Security Employee Social Security Employer Belgium 55.3% 21.6% 10.8% 22.9% Sweden 42.7% 13.5% 5.3% 23.9% USA 31.7% 16.5% 7.0% 8.1% UK 30.8% 12.8% 8.4% 9.7% Ireland 27.5% 14.2% 3.6% 9.7%
The rest of the 500+ page report goes into more detail, for example on second earners, or families with children, or different wage levels. On page 548, among the limitations of the report, it says
Employers' contributions to private pension, family allowance or health and life insurance schemes are excluded though the amounts involved can be significant. In the United States, for example, these contributions can account for more than 5% of the earnings of employees.
I suspect it also excludes employees' private contributions, but does not see these as potentially part of a wedge between gross labour costs and net pay. So a country which funds these through taxes or social security might be expected to have a higher tax wedge than one which does not.