When scientists measure, what system do they use?
The metric (or SI) system.
Scientists around the world agreeably use the same system to lessen complications, and the system is called the metric system, using meters, kilograms, seconds, etc. as base measurements.
The modern form of the metric system is called the International System of Units (frequently abbreviated to SI), having seven base units: kilograms (mass), meters (length), seconds (time), amperes (electric current), moles (quantity), candelas (luminous intensity), and Kelvin (temperature).