The Ecological Footprint for the United States is 8.1 gha per person (in 2018) and global biocapacity is 1.6 gha per person (in 2018). Therefore, we would need (8.1/ 1.6) = 5.1 Earths if everyone lived like people living in the United States.

I had to hit the glossary, so sharing it here:

global hectare (gha)
Global hectares are the accounting unit used in Ecological Footprint and biocapacity accounts. These productivity-weighted, biologically productive hectares allow researchers to report both Earth’s (or a region’s) biocapacity and the demand placed on it (the Ecological Footprint).
A global hectare represents one hectare of biologically productive land with the world’s average biological productivity for a given year. Using this unit, rather than merely hectares, is necessary because different land types have different productivities. For example, one global hectare of cropland would occupy a smaller physical area than pasture land, which is typically less biologically productive. This means that typically more pasture would be required to provide the same biocapacity as one hectare of cropland.
Since global productivity varies slightly from year to year, the value of a global hectare also changes slightly over time.
Because global hectares are commensurable, they can be aggregated, enabling comparisons across activities, time, and regions. Note that areas with very low productivity, such as deserts, ice fields, or the open ocean, are excluded from the accounts.