Do airliners have sensors to measure their takeoff weight, or is it just calculated by reference to known values?

Airline dispatcher here. The takeoff weight of an aircraft is calculated by adding the weight of the aircraft itself (OEW - Operational Empty Weight), the payload (passenger/baggage/cargo), and the fuel together. The only weight that the aircraft itself calculates by itself is how much fuel is in the tanks at a given time. The OEW is based on the weight of the plane itself plus things like catering, crew members, and fluids. Depending on the flight, the OEW can be different as some flights carry less/more catering, etc. Any time major changes or maintenance is done to the aircraft, it's OEW is revised. Each aircraft in an airline's fleet has it's own OEW as not every plane will weigh the same even if it's an identical model. The payload and fuel weight are variable. Airlines use a set figure for each male, female, and child on the flight (based on historical data from weight surveys or based on the regulatory authority in the country of registry). Baggage weights are based on the weight of each checked bag (for planning purposes we use an set weight per passenger). The actual weight of all the checked bags is given to the captain via the ground staff. If the flight has cargo, the exact weight is also considered to be part of the payload. The amount of fuel required is calculated by the flight planning system and takes into account factors like distance, winds, route, taxi time, and any additional fuel given by the dispatcher for navigating around weather/holding at the arrival airport due to bad weather/etc.