The replacement ratio for the euro zone as a whole is 54%.

WSJ: Public-Sector Strikes Hit European Holiday Travel

The replacement ratio needs to be higher than average for the least well paid, who spend proportionately more on essentials such as food, fuel and shelter.

ECONOMIST: Falling short

The net result: Most people end up targeting about 70% to 80% of their pre-retirement income, which basically represents 100% of their pre-retirement spending (in fact, this is where the "replacement ratio" approach to determining retirement income originated).

WSJ: The Experts: How to Plan for Retirement Expenses

For all developed countries, high life expectancy is also associated with below-replacement fertility, which reduces the ratio of workers to retirees.

FORBES: Healthcare Sector is a Natural Hedge for Pension Funds

And there is Tobin's q, a ratio of the stockmarket value to the replacement cost of its tangible assets an attempt to measure what it would cost to recreate a company from scratch.

ECONOMIST: A survey of global equity markets: Valuation waltz | The