Flat dimensions are the length, width and height of an empty box or case before it's packed. They're typically measured along the flat sides or edges. In some cases, the flat dimensions are printed on the box or case.

Filled dimensions are the length, width and height of the outermost points of a box or case after it's been packed. These measurements include any bulges, bowing, handles, wheels, straps and other features that extend beyond the flat sides.

Filled dimensions are what carriers measure when they scan your shipment in transit, and they're the dimensions you should enter when booking on Bikeflights.com to help avoid carrier adjustments.

The key difference is that filled dimensions account for the bulging that naturally occurs after packing, while flat dimensions do not.

Think of it like a bike tire: a tire's advertised width isn't necessarily its actual installed width. You don't know its true width until it's mounted on a rim. Likewise, you won't know the true dimensions of your box or case until it's packed.