You can feed yourself off of one acre, with primitive tools and basic agricultural practices. There are 1.9 Billion acres in the USA alone. With modern agricultural technology and power of scale, the resources in the ocean, you can feed a lot of people.
This site has statistics showing that despite the population increase, the total amount of acres of farmed farm land has decreased in the last 20 years in the USA.
Its about 900 million.
https://www.statista.com/statistics/196104/total-area-of-lan...