Generally the computer / flight crew does those calculations based on location of passengers, cargo and fuel. They probably missed something and requested more

Generally the computer / flight crew does those calculations based on location of passengers, cargo and fuel. They probably missed something and requested more weight. Source: I was personally loading cargo on an Embraer 175 two days ago. Also this link gives a good overview of weight sensors in planes. https://aviation.stackexchange.com/questions/1850/do-some-airplanes-have-weighing-scales-on-the-landing-gear https://aviation.stackexchange.com/questions/1850/do-some-ai...