Scots would have been the equivalent of £2,390 per head better off than the United Kingdom as a whole in 2012, based on the SNP administration's calculation of Scottish GDP.
UK GDP was £21,466 per head in 2012 according to the Organisation for Economic Co-operation and Development (OECD) while the Scottish Government's application of OECD methodology puts Scottish GDP at £23,856 per head.
Finance Secretary John Swinney said: "With the powers of independence we would be able to harness that wealth for the benefit of people in Scotland.
"Seven of the top 10 countries in the OECD have populations of less than 10 million people, demonstrating what can be achieved by small independent countries with the powers to manage their own economies.
"Scotland has five of the world's top 200 universities, a booming food and drink industry worth over £13 billion a year, a huge market for tourism, 25% of Europe's offshore wind and tidal energy and growing potential in areas like life science, low carbon manufacturing and in our rural and island economies."
The OECD revised its GDP methodology for 2012 to take account of purchasing power, which caused the UK to slip two places to 18 compared with the previous year.
The new methodology means Scotland has slipped six places since the publication of the Scotland's Future white paper and eight places from a similar analysis conducted in 2010.
A Scottish Government spokesman said Scotland and the UK's position would have been unchanged if the OECD methodology had been consistent across the three years.
The OECD said it cannot endorse or comment on the Scottish Government's figures as it only analyses the GDP of existing OECD countries.
Scottish Conservative finance spokesman Gavin Brown said: "We were told categorically in the White Paper that a separate Scotland would be the eighth wealthiest country in the OECD.
"Have we slipped six places in the last three months or will the Scottish Government admit that the White Paper calculations were simply untrue?"
Scotland was ranked the 19th wealthiest nation by the Financial Times, compared to the UK in 23rd place, while ratings agency Standard and Poor's has said Scotland would qualify for its "highest economic assessment".