Do pilots of civil aircraft know the exact weight of the aircraft prior to take-off?
No, not the exact weight.  They estimate the likely weight, with a margin for error, and on more modern aircraft (like the A330), onboard software will calculate the actual weight once airborne and then suggest the optimal angle of attack for the flight.
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Answer the following query.
Do pilots of civil aircraft know the exact weight of the aircraft prior to take-off?

user
No, not the exact weight.  They estimate the likely weight, with a margin for error, and on more modern aircraft (like the A330), onboard software will calculate the actual weight once airborne and then suggest the optimal angle of attack for the flight.
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