Gram for gram, beef costs more to produce—in land, water, and greenhouse gas emissions—than most fruits and vegetables. That’s inspired some environmentally minded scientists to call for a drastic reduction in the number of cattle raised for milk and meat. But it wouldn’t be good to do away with them entirely—they create much of the fertilizer we use, and they consume huge quantities of plant waste, such as corn stalks and distillery grains. So what amount of bovines is “just right”? To find out, researchers first imagined a world in which cattle lived only off plant waste and grass—not crops planted specially for them. If the land devoted to growing food for cattle in the United States were used to grow peas, barley, and other crops for people instead, beef production would drop by 55%, from 31 million to 14 million beef cattle, the team reports today in Nature Ecology and Evolution. Of course, that would result in another drop—in the amount of beef we consume. To achieve this grass-fed utopia, Americans would need to cut their beef intake by more than half, from 460 grams per week—the equivalent of one 16-ounce steak—to about 207 grams. Even at that rate, U.S. beef intake would still be double the global average—on par with South Africa and South Korea.