This was an increase of five per cent in the year and more than double the figure in 2002.
Towers Watson's Global Pensions Assets Study looked at the 13 largest pension markets which account for 85 per cent of global pension assets.
The UK is now ranked as the third-largest pension market, behind the United States and Japan.
Ten-year figures show the UK and Netherlands both grew their pension assets the most as a proportion of GDP.
Equity allocations for UK pension funds fell from 61 per cent in 2002 to 45 per cent in 2012. Pensions' exposure to alternative assets in the UK increased from three per cent in 2002 to 17 per cent.
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Global institutional pension fund assets overall increased by nine per cent and Towers Watson said the growth was a continuation of a trend in global assets which began in 2009.
Chris Ford, EMEA head of investment at Towers Watson, said: "Given the extreme economic and market volatility we have experienced during the past five years it was a relief for many pension funds to finish the year in better shape than when it started, for a change.
"While volatile markets are expected to continue for the foreseeable future, pension funds are now generally better equipped to deal with them."
Mr Ford said more funds had begun to deal with their pension governance shortfalls by appointing more qualified people or outsourcing the portfolio management to a third party.
In addition, pension funds were implementing more flexible investment strategies to make allowance for extreme events.

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