The total weight of your Main Weapon + Armor + Sub Weapon is your 'Battle Weight'. Your Strength is your threshold; exceed that threshold, and for every 1 point you exceed it by, you suffer -2 Evade and -2 Hit. (You do not receive any benefits for going under.)
Some materials, namely Galdric (which reduces weight), and certain enchantments (namely Floating), have gotten better because they can dramatically reduce your Battle Weight.
Your Battle Weight is displayed below your HP and FP; the number on the left is your current Battle Weight, and the number on the right is your threshold. So 5/12 BW would mean you were under your maximum before you began taking penalties. While 24/20 would mean you are 4 over, meaning you suffer -8 Hit and -8 Evade.
| Power vs. Protection|
Hit vs. Evade
Critical vs. Critical Evade
Status Infliction vs. Status Resistance