How does worldometers website calculate the stats?

If you visit to 'About' page of worldometers website then you would get its complete detail, like how they develop it, how they update it and how it functions overall etc.

The subject website has mentioned as, "collect data from official reports, directly from Government's communication channels or indirectly, through local media sources when deemed reliable."

It runs by an international team of developers, researchers, and volunteers with the goal of making world statistics available. They are completely independent and self-financed through automated program to execute the data / statistic updates.

In addition, that website gives various related links under "Sources" section as well.

Their website is https://www.worldometers.info/. They are giving statistics about various issues and they are supposed to be very realistic.
As per their website they are giving these statistics to various organisations which include. Oxford University Press, World Wide Web Consortium (W3C), The Atlantic, BBC, Morgan Stanley, IBM, Hewlett Packard, Dell, PricewaterhouseCoopers, Google Translate and many other. They have a team having members from various countries. The members are from developers, researchers, scientists and volunteers. They claim that their data is very accurate and they work independently and have contacts everywhere to get the rea; time statistics from various sources.

Worldometer was established by Andrey Alimetov, a Russian immigrant to the United States. It has got popularity as one of the biggest free source of information about world population, government, economics, society, media, environment, food, water, energy, and health etc. It is part of the Real Time Statistics Project, and is organized by an international team of developers, researchers, and volunteers. It is available in 34 languages. In 2020, the website obtained enormous popularity because of hosting statistics pertaining to the COVID-19 pandemic.

Their data, invariably, is considered as reliable and authentic, and used by the UK Government, Johns Hopkins CSSE, the Government of Thailand, the Government of Vietnam, the Government of Pakistan, Financial Times, The New York Times, Business Insider, BBC etc.

They compile and considerable updates per minute are conducted by their smart team of analysts and researchers who substantiate and verify the data from an ever-growing list of over 5,000 sources which include Official Websites of Ministries of Health or other Government Institutions and Government authorities' social media accounts, press briefings' live streams throughout the day etc.

Worldometer collects, validates and aggregate datas from the different sources and even provide COVID 19 live statistics for a wide audience around the world. Such datas are trusted and used by UK Government, Government of Thailand, Government of Vietnam, BBC and many others.
Before Pandemic, Worldometer was best known for its reliability in terms of figure such as population of the world, number of cars produced in a year and license counters in different countries.
With the COVID crisis, its popularity has boosted to an astonishing level since it is providing top ranking Google results for the Corona Virus Statistics.
The figures are continuously fed by the experts engaged in researching and Volunteers having goals to provide the latest statistics in varied cases where the collection of the datas was primary concern.
The figures relating to COVID 19 cases may be somewhat less such as hospitalisation, deaths of the patients since the datas fed by New York, Texas, Jersey, Washington etc are not the true revealation soft figures.
Hence both the Worldometers and John Hopkins number may be inflated figures.