Calls for JPMorgan Chase & Co. Chairman Jamie Dimon to relinquish the chairmanship have mounted since last May, when New York-based JPMorgan disclosed risk-control lapses in its chief investment office on credit-derivative bets that fueled a $6.2 billion trading loss and sparked regulatory probes. Photographer: Chris Ratcliffe/Bloomberg
Calls for JPMorgan Chase & Co. Chairman Jamie Dimon to relinquish the chairmanship have mounted since last May, when New York-based JPMorgan disclosed risk-control lapses in its chief investment office on credit-derivative bets that fueled a $6.2 billion trading loss and sparked regulatory probes. Photographer: Chris Ratcliffe/Bloomberg

It's as official as it's going to get for now: JPMorgan Chase & Co. is the world's largest bank by total assets, using the best available data for apples-to-apples comparisons.

Differences in global accounting standards historically have made size comparisons between U.S. and overseas banks difficult. Companies that use the International Accounting Standards Board rules to prepare their financial statements must show gross values for derivatives and certain other types of financial instruments. Companies that use U.S. generally accepted accounting principles have been allowed to report smaller net values for the same things.

From now on, though, U.S. companies are required to disclose gross numbers for those items in the footnotes to their quarterly reports, under new rules from the U.S. Financial Accounting Standards Board. The comparisons between companies aren't perfect, but they're good enough for these purposes.

The end result: JPMorgan said it had $2.39 trillion of total assets as of March 31 under U.S. standards. On a gross basis, that would have been slightly more than $4 trillion, or about 20 times common shareholder equity, according to the numbers in the quarterly report JPMorgan filed last week.

The vast majority of the difference stems from the way JPMorgan reports derivatives. On a net basis, the company showed $70.6 billion of derivatives on the asset side of its balance sheet. Meanwhile, the gross value was $1.53 trillion. U.S. accounting rules let banks offset huge chunks of their assets and liabilities against each for financial-reporting purposes -- hence, the big gap between the gross and net numbers.

The $4 trillion figure easily puts JPMorgan ahead of Industrial & Commercial Bank of China Ltd., which showed 18.36 trillion yuan ($2.96 trillion) of total assets on its March 31 balance sheet. ICBC is the largest bank that uses international accounting rules, according to data compiled by Bloomberg. Europe's largest bank, Deutsche Bank AG, showed 2.03 trillion euros ($2.61 trillion) of total assets as of March 31, under international rules.

One caveat: Tokyo-based Mitsubishi UFJ Financial Group Inc. uses U.S. standards in its reports with the U.S. Securities and Exchange Commission. It has yet to release results for the year that ended March 31. So it hasn't begun disclosing gross values for its financial instruments. Mitsubishi UFJ showed total assets of 224.5 trillion yen ($2.59 trillion) as of Dec. 31, 2012, using Japanese accounting standards. We won't know for some time whether Mitsubishi winds up being bigger than JPMorgan using the gross-asset numbers from its footnotes.

(Jonathan Weil is a columnist for Bloomberg View. Follow him on Twitter.)