Summarize this article in one sentence.
The GDP of a country is the measure of goods and services produced within a specific time period. You'll need that number to calculate productivity based on GDP.  You usually won't have to calculate the number yourself (that would be very difficult). Instead, you can find the number already calculated for you. You should be able to find the GDP of most countries online. Start by Googling the country's name plus "GDP". You can also find the GDP of many countries at the World Bank website.  Make sure you find the right GDP for the time period that you're measuring (e.g., for a quarter or a year). Keep in mind that the GDP number for the target country, even if it's released for a quarter, might be given as an annualized number. In that case, divide the annualized number by four to get the quarterly number. Basically, you're calculating the number of so-called "man-hours" worked to produce products and services. For any country, find the number of people in the workforce for the given period and multiply it by the average number of hours worked.  For example, if the average number of hours worked is 40 and there are 100 million people in the country, then the total productive hours is 40 x 100,000,000 or 4,000,000,000. In the United States, you can find the key statistics on the website of the Bureau of Labor Statistics (BLS).  Labor productivity for other countries can be found by searching online for relevant economic research. Just divide the GDP by the total productive hours. The result will give you the productivity for that country. For example, if the country's GDP is $100 billion and the productive hours are 4 billion, then the productivity is $100 billion / 4 billion or $25  of output per hour worked.

Summary:
Determine the country's Gross Domestic Product (GDP). Calculate the number of total productive hours for a country. Calculate productivity.