How many bottles of wine are there in the world?

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Dear Dr. Vinny,
While I was drinking a bottle of wine recently, my 7-year-old stepdaughter quizzically asked, “How many bottles of wine are there in the world?” So—for the kids—how many bottles of wine are there in the world? (An approximate number is acceptable.)
—R.V., Nijmegen, Netherlands
Dear R.,
Sure, anything for the kids.
It’s easiest to answer the question by converting everything into standard 750ml bottle sizes. In that case, according to the very smart folks at our sister publication Market Watch, 31.4 billion bottles are bought and sold worldwide every year. And according to the Food and Agriculture Organization of the United Nations, the equivalent of 36 billion bottles of wine are produced worldwide each year.
That still doesn’t tell us how many bottles are in actual existence—just because a bottle is bought or sold doesn’t mean it’s been drunk, and we don’t know how many bottles are resting on wine shop shelves, let alone in people’s cellars. And though we’re choosing to convert the volume of wine out there into standard-size bottles, the truth is that wine is also sold in boxes, Tetra Paks and even casks, for wines on tap.
So I’ll leave you with that information and let you decide what to tell the kids. An approximate number is acceptable.
—Dr. Vinny