Americans work among the most hours of any advanced economy, save Korea, where stressed out workers have begun checking themselves into prison-like institutions to get away from it all, and Japan, where they’ve invented a word for death from overwork: karoshi.

Americans also work among the most “extreme” hours, which the Organization for Economic Cooperation and Development defines as 50-plus hours a week. It’s a trend that’s been accelerating among white-collar workers since the 1980s, especially once Silicon Valley programmers started pulling all-nighters and wearing T-shirts boasting “90 Hours a Week and Loving it.”

But let’s face it, the official record of hours worked doesn’t tell the whole story of our work-worshipping, workaholic culture. What’s missing? All the “after-hours” unpaid, off-the-clock face time you put in at the office because the boss is still there, or because everyone else is still there, some deadline is looming, or you’re afraid you’ll be seen as deadwood if you leave first. The Japanese also have a word for this: furoshiki, “cloaked overtime.”

What else is missing from those work hour calculations? All the time on technology, the stolen evenings answering texts and calls, the e-mails that come in at 11 p.m., 3 a.m., 5 a.m. The constant feeling of being tethered to the office and always “on call.”

Even so, you can almost hear the chorus of rationalizing, if exhausted, protest in workplaces throughout the land: “Yes, but isn’t putting in all those hours just what it takes to be No. 1?”

That’s why the OECD’s annual measure of productivity is so eye-opening, No, it turns out, it doesn’t. Long hours, in some cases, are a drag on hourly productivity, not to mention efficiency and innovation. Take Japan and South Korea, for instance, which hover close to the bottom of the hourly productivity rankings despite the meditation prisons in Korea and workers dying at their desks in Japan.

Some years, Norway, Luxembourg and Ireland rank higher than the United States in hourly productivity. Germany, which has a policy of “Kurtzarbeit” or short work hours in order to spread the work around and reduce unemployment, is highly productive by the hour.

And the country whose productivity in many years rivals the overworked United States? France. Yes, France. Where workers enjoy 30 days of paid vacation every year (the United States is the only advanced economy with no paid vacation policy), generous social supports (the cost of a maid is tax deductible!), and, as one recent controversial commercial put it, a leisurely stroll to the café after leaving work at a decent hour.

Denmark, a country I visited while reporting “Overwhelmed: Work, Love and Play When No One Has the Time,” a book on time pressure and modern life, is not only one of the most productive, but also one of the happiest. (The United States, in contrast, is ranked by the World Health Organization as the most anxious.) In Denmark, I was told, no one is rewarded for working long hours, and the boss is often the first out the door. “Here, if you can’t get your work done in the standard 37 hours a week,” one Dane told me, “you’re seen as inefficient.”

Something to think about when you find yourself sitting at your desk late at night, waiting for the boss to leave, or returning a work e-mail when instead you should be fast asleep.