There are many different ways to measure the size of a company. Besides stock market capitalization, revenue may be the most straightforward metric to understand the relative importance of a business.

Investors can track the Fortune 500 as an annual ranking of the biggest corporations in the United States by their sales of goods and services. The regularly changing list can offer insight into how industry leaders are growing and which high-level themes are shaping the economy.

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The list below shows the five biggest US companies by revenue in 2019.

Data source: Fortune 500.

The latest ranking based on 2023 revenue features four of the same five names, but there have been some important changes.

Walmart is still on top as the largest US company, but Amazon is fast on its heels. The e-commerce leader has more than doubled its top line since 2019 to climb into second place. Energy giant Exxon Mobil fell off the list and was replaced by healthcare leader UnitedHealth Group (UNH 1.23%).

Data source: Fortune 500.

A key takeaway is that technology is playing a bigger role across multiple sectors.

Walmart, for example, is investing heavily in its own e-commerce capabilities to better compete with Amazon. UnitedHealth incorporates tech through its mobile app and offers virtual care services to improve the patient experience. Even financial conglomerate Berkshire Hathaway is recognized as a leader in areas like insurance and fintech, which are benefiting from ongoing digital transformation.

Expect the list of the biggest companies to continue evolving and further blur the lines between traditional sector classifications thanks to technology.