Beech 1900
Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 300; Flight Crew Total 1040; Flight Crew Type 400
Situational Awareness; Training / Qualification
Deviation / Discrepancy - Procedural Weight And Balance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Human Factors
After delivering freight to station agents in ZZZ; we were tasked with loading backhaul for the return flight to ZZZ1.  Weight for each box [of cargo] as well as a total weight manifest was provided to our station agent; which should have been actual (gross).  Based on this manifest; the captain calculated weight and balance to assess the amount of [cargo] that could be safely loaded while the first officer prepared the aircraft for loading.The captain advised the first officer of the amount to be placed in each loading zone.  Loading commenced thereafter and though highly subjective; each box appeared to have a standard weight as experienced throughout several similar revenue flights.  The amount of boxes per loading bay seemed uncharacteristically high; however; after revisiting the manifest; the numbers added up and no reason existed to have any further doubts as to its accuracy.Fully loaded; we departed on an IFR clearance back to ZZZ1 using speeds for the calculated weight.  The aircraft did not handle out of the ordinary during any phase of flight offering zero evidence that loading may have been incorrect.  Landing in ZZZ1 was equally uneventful.In ZZZ1; company agents also felt that the number of boxes onboard exceeded normalcy and decided to perform a secondary weighing.  The result solidified fact that we were given incorrect information in ZZZ to our detriment.  The weight observed in ZZZ1 determined that net weight was calculated in lieu of gross weight when preparing the manifest.  This; of course; does not account for tare weight thus omitting an average of 10 pounds per box.  With approximately 90 boxes on board; the maximum weight allowable under the circumstances was exceeded by 900 pounds.Though the flight concluded safely; any power-plant anomaly could have rendered the aircraft unflyable; consequently leading to the death of all on board.  Gut feeling on the part of the first officer should have mandated a reweighing of the cargo before departure; however; facility agents tasked with providing accurate weight information to the crewmembers they serve should be heavily scrutinized in this instance as well.  Furthermore; it was discovered that another crew had experienced a similar incident out of ZZZ; this incident; if disseminated throughout the pilot cadre; may have proved useful in the overall decision-making process.The crew made an incorrect calculation (and by proxy decision) based on a fallacious culture of trust between operational entities.  However; it may be beneficial to ensure station agents are confirming the weight of cargo received before providing such information to busy; possibly tired flight crews as this incident occurred outside of the normal circadian rhythm of the human clock.
A BE1900 First Officer reported taking off about 900 lbs over maximum allowable weight when their weight and balance was improperly calculated.