Imagine finding five grocery bags full of plastic on every square foot of coastline, in every country that borders the sea. That is the amount of plastic entering the world’s oceans every year, according to a new report.

The millions of tiny bits of plastic enter the ocean and are carried by currents into every area and every ecosystem in the ocean. Researchers have suspected that most of it began as waste on land, but the amount of trash finding its way into the ocean has never been confirmed.

Now, a team of researchers have put a number on the trash going into the sea and published their findings in the February 13 edition of the journal Science.

The researchers estimated that between 4.8 and 12.7 million metric tons of plastic are entering the sea annually, all generated by people living within 31 miles (50 kilometers) of the coastline. In the year the study was conducted, 275 millions metric tons of waste was generated in the 192 countries bordering the sea, providing a percentage of the amount making its way into the water.

“Until now, we have been estimating the amount of plastic pollution in the ocean by taking a ship far offshore, towing a plankton net, and counting each individual piece of plastic collected. This is a very tedious and expensive task,” said Kara Lavender Law of Sea Education Association (SEA) and principal investigator of the NCEAS marine debris working group, in a statement.

For the new study, the researchers used a different approach. They began looking at debris of any kind entering the ocean through any pathway. They developed models for each of the sources of pollution and then began looking for plastic.

In addition to finding out how much plastic went into the oceans, the researchers were interested in where it was going. With a midpoint of roughly 8 million metric tons going in, the researchers were finding only 6,350 to 245,000 metric tons, a maximum of three percent of the total waste, floating on top of the water.

“This work gives us a sense of just how much we’re missing, how much we need to find in the ocean to add up to the total. There is a lot of plastic sitting on the bottom of the ocean and on beaches worldwide. Right now, we’re mainly measuring plastic that floats, and only in relatively few locations,” said Law.

According to Jenna Jambeck, an assistant professor of environmental engineering at University of Georgia and the study’s lead author, the cumulative input of plastic waste to the oceans will equal 155 million metric tons by 2025. However, according to World Bank calculations, the planet will not reach “peak waste” until 2100.

“We’re being overwhelmed by our waste. But our framework allows us to also examine mitigation strategies like improving global solid waste management and reducing plastic in the waste stream. Potential solutions will need to coordinate local and global efforts,” said Jambeck.

SEA scientists and undergraduate students add to the plastic debris data annually through research trips.

“The several thousand SEA Semester students who have collected and counted plastic debris since the 1980s have been essential contributors to our understanding of the scale and scope of this pollution problem,” said SEA president Peg Brandon.