Each country has its own system of calibration standards. However, the most widely accepted calibration standards are set and maintained by the International Bureau of Weights and Measures.
The International Bureau of Weights and Measures has set and maintained calibration standards since 1875, when the original 17 participating countries signed a document called the Metre Convention or the Treaty of the Metre. As of 2015, there are 51 countries that have signed the Metre Convention.
The United States signed the Metre Convention in 1878, but also maintains its own measurement standards department called the National Institute of Standards and Technology, or NIST.