Most airlines allow bags to weigh up to 50 pounds without additional charges. Go above that and you'll pay anywhere from $25 to $150, even if your bag is over one ounce. The average fee for overweight bags is somewhere between $50 and $60.
With that much cash on the line, should you trust the airport scales?
ABC7 went to the three Bay Area airports to test the scales ourselves, without letting anyone know what we were up to in advance.
We began at the Department of Weights and Measures in Contra Costa County. ABC7 purchased a large pound of sand, removing some until the suitcase we placed the bag in weighed exactly 50 pounds.
At the Mineta San Jose International Airport, ABC7 checked over a dozen scales. One scale read exactly 50 pounds, as did the baggage scale next to it. ABC7 then checked several different scales at counters belonging to different airliners and found they measured 50 pounds of weight as well.
"Awesome," said passenger Alan Jorzak of Chicago. "You would think they might try to swindle you a little bit."
The same result was seen at San Francisco International Airport -- every scale ABC7 measured weighed exactly 50 pounds.
At Oakland's International Airport, two scales underweighed the bag -- one by nearly half a pound and another by one-tenth of a pound. By and large, though, Oakland's scales also measured the bag accurately.
One scale did read the bag as overweight, but once we shifted the contents around, the bag weighed in at exactly 50 pounds.
If a scale does read a bag as overweight, try rolling the bag back and forth on the scale. The contents may shift, which could lead to a better weight reading. If the scale still reads the bag as overweight, try weighing it on the scale next to it.
Airline scales, just like scales in your local supermarket, are tested and certified by each county's weights and measures department.