It took nearly a half-century, but scientists finally have a handle on how much plastic enters the open ocean every year. The last estimate was in 1975, when a National Academy of Sciences study hazarded a guess that about 0.1% of global plastic production sweeps out to sea annually. Now, researchers say reality is much grimmer. The team looked at how much plastic waste every coastal country in the world produces and estimated how much of it could potentially spill into the sea because it ends up as litter or in open dumps and leaky landfills. The scientists figured roughly 15% to 40% of that littered or dumped plastic enters the ocean each year. Adding together all 192 countries in the world with a significant coastal population, the researchers report online today in Science that about 4 million to 12 million metric tons of plastic washed offshore in 2010 alone, or about 1.5% to 4.5% of the world’s total plastic production—enough to cover every foot of coastline on the planet. That’s just the beginning of the problems, the team says, as scientists still don’t know where more than 99% of ocean plastic debris ends up—and what impact it’s having on marine life and the human food supply. What’s more, the authors predict that the annual amount of plastic waste tumbling out to sea will more than double in the next 10 years.