Charge bonus

Some weapons, usually lances, have the Damage Bonus on 1st Attack tag, commonly referred to as the charge bonus.

Charge bonus: Size + (Combat Speed / 4)

Charge bonus for flying units: Size x2

Max bonus: The bonus damage is capped at Strength / 2.
If the weapon has the Higher charge bonus cap tag the cap increases to Strength.

Note that single use lances like the Heavy Lance are retained until the weapon hits. This includes Shield parries, making shields especially suitable for blocking lance charges.
Flying units do not use combat speed based calculation even if that would have been better.
Weapons with the Higher charge bonus cap also have the one-use-per-battle tag meaning that they can only be used once. If the unit misses, the weapon is still lost.
Most weapons with the Higher charge bonus cap are also two-handed weapons which means that they get 125% of Strength added to the damage roll instead of the usual 100%. This also raises the potential charge cap.
Testing has shown that units with charge bonus do not gain a charge bonus vs flyers.
This needs further testing. First, it appears that this may be limited to innate flying, not in-battle effects like Gift of Flight. Second, flyers may be able to get a charge bonus against other flyers.