Can someone explain the Great Weapon Fighting style feat?

Does the effect apply to all dice or just one?

When you roll damage for an attack you make with a Melee weapon that you are holding with two hands, you can treat any 1 or 2 on a damage die as a 3. The weapon must have the Two-Handed or Versatile property to gain this benefit.

It affects all of your dice on the attack. So if you attack with a Greatsword, the affect applies to both dice. It also applies to anything that might add damage to the attack, such as Sneak Attack, Hex, or the extra damage from a magic weapon like a Flame Tongue Greataxe.

I will point out, that this damage bonus sounds better that it actually is. The average die roll for a d6 will only change from 3.5 to 4. The damage increase gets even smaller as the size of the die goes up. On a d12, it is only 0.25 more average damage per die.

Thanks!

I am not entirely convinced that's correct. The Feat affects the weapon damage rolls, but i'm not sure it also affects additional damage from other sources. Will need to research it more.

Quote from HarmAssassin >>

I am not entirely convinced that's correct. The Feat affects the weapon damage rolls, but i'm not sure it also affects additional damage from other sources. Will need to research it more.

It was clarified in Sage Advice here that it does not apply to dice from add-on damage effects like Hex.

That said, in practice a lot of DMs (including me) would probably allow it to apply to things like that, because otherwise it's a pretty garbage feat.

Garbage might not be the right word. It takes you minimum damage with normal great sword from 2+mods to 6+mods. With extra attack that stacks quickly with some decent damage each hit. Also the goes crazy at low levels. If you have a +3 in strength then you deal minimum of 9 damage per hit which is a definite one shot of a goblin minion. It removes the chance of not on taping low hit point monsters. If you multiclass to Ranger or warlock and grab hex/hunters mark that adds another 3 on there. Seem at least ok to me.

Get a vicious weapon. I like the maul. A vicious maul does 4d6 damage. Vicious weapons are Rare, meaning it can be crafted with just 2000gp and 25 days of downtime, assuming you have proficiency in arcana, proficiency with smithing tools, and the means of hiring an assistant or getting a party member with the same proficiencies to help.

With Great Weapon Fighting, that means you do a minimum of 12 plus strength modifier per hit. And if you have the weapon mastery for the maul, your target must make a CON save or end up prone. As you likely won't be able to afford this weapon until after level 5, you will have a second attack, which will often be made at advantage if your first attack connects. Both attacks hitting in one turn is a minimum of 24 damage plus strength modifier x 2 (a 20 STR makes this a minimum of 34).

Looking at a few common solo CR 6 monsters, (Wyvern AC 14 HP 127 CON +3; Chimera AC 14 HP 114 CON +4, Young White Dragon AC 17 HP 123 CON +4) a fighter with this weapon and this feat can do 25 to 30% of HP damage in a single round and has a decent chance of knocking them prone for other melee attackers (a 20 STR at level 6 is a CON DC of 16)

This feat, when used with the right weapon and with right build, is anything but garbage.