© Wizards of the Coast by Anna Podedworna

Great Weapon Master Feat 5e: We Ran The Numbers On When To Use It

In the worlds of Dungeons & Dragons, there may be nothing more exciting than choosing your weapon. The weapon we decide upon when we build our character will set the course of our adventure.

For those who wish to make a show of their strength at every turn, a heavy weapon is the way to go. When your character wields one of these it is clear to anyone in their path that they are not to be messed with.

Not only are heavy weapons massive, but they pack a punch. Often they are the weapons likely to deal the most damage in the game. 

Of course, there’s no such thing as too much damage.So if you’re looking to make your heavy weapons hit that much harder, check out the great weapon master feat.

How Does Great Weapon Master Work?

The great weapon master feat is evidence of your character’s work at mastering their skills in heavy weapons and melee combat.

It gives you access to extra attacks and even lets you deal more damage, at a cost.

  • On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
  • Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.

The first ability is great for a weapon that’s going to be dealing as much damage as this does. An extra attack is always a great thing to gain, and the conditions aren’t too hard to meet.

Even if you’re only getting a bonus action attack once per combat that’s still a good extra bit of damage. 

It’s also noteworthy that the first ability only specifies a melee weapon attack. There are no requirements to take this feat, so if someone has the great urge for this feat while they’re using a non-heavy weapon they can.

It’s not suggested, because we don’t want to pick up a feat for half of its abilities, but it’s possible. 

The other ability of this feat is where a great weapon master really starts to shine. Taking a penalty to your attack roll for the potential to almost double your attack’s damage is pretty impressive.

This isn’t the only feat that gives character’s this ability. Ranged weapon combatants get to make the same tradeoff with their ranged attacks thanks to the sharpshooter feat. Both feats give you so much potential damage. 

Weapons that Work with Great Weapon Master

In RAW, the melee weapon types that have the heavy property are as follows:

  • Glaive
  • Greataxe
  • Greatsword
  • Halberd
  • Maul
  • Pike

Getting the Most Out of Great Weapon Master

If you pick up this feat it’s a sure fact that you’re going to be dealing a lot more damage, even if you only end up using the bonus attacks. However, as with any ability that gives us a choice, we need to decide when to use it.

The first ability is a given. You’ll get the most out of it by getting lucky on dice rolls and by dropping opponents to 0 HP.

Advantage is just about the only thing that can make natural 20’s more likely, so if you can generate that you’ll trigger this ability more often. Otherwise, plan your strikes well.

As for the second ability, most players get really excited by that +10 to damage, as you should. Here’s the thing though, you don’t really want to be using this all the time unless you’re a big gambler. A penalty of -5 is also a lot, that’s a quarter of a d20 roll. 

You have to have some way to compensate for the -5 to really make it worth it. Let’s remember that we’re rarely ever just rolling a die. We normally have our proficiency bonus and our ability modifier on top of the roll. If we have +5 between those, then we’re at least canceling out the penalty.

Of course, that’s still not great. At this point, we’re at least rolling the die with no visible penalty, but that leaves us purely at the mercy of the odds. We should probably wait to take this feat until we can consistently have a modifier to our dice rolls that are greater than +5. 

Most character’s taking this feat should wait until 8th level to take this feat, since at 9th you’ll have a proficiency bonus of +4. Then you’re just reliant on your ability bonus and any bonuses your weapon itself might provide.

If you can be somewhere around +8 or +9 (+3 or +4 with the penalty) then you should be doing rather well whenever you choose to use this feat.

All that being said, if you can reliably create advantage, get another bonus to your attack roll, or somehow improve your odds of hitting then this feat becomes better and better.

What AC Should I Use Great Weapon Master for?

Normal Attack: Target’s AC Attack Modifiers + 5.5

Advantage Attack: Target’s AC Attack Modifiers + 8.825

Everybody wants to know when they should choose to use this feat’s penalty and try to get the bonus damage, so I’ve taken the time to do the math. I was going to throw this in the FAQ below, but there are a lot of factors. 

Let’s start with when not to use this. If you have disadvantage, don’t have an idea of the target’s AC, or can drop the target to 0 HP with an average attack of your normal damage, don’t try to get bonus damage.

Always find the target’s AC first so you know what you’re dealing with. Disadvantage is a pretty obvious reason to not take a penalty. And then, if you can take them out, there’s no reason to risk a miss.

If you want to understand the math, keep reading. Now, let’s talk about dice rolls. On average, a d20 rolls 10.5. This is because each outcome is equally probable (5% chance), so the average of all the outcomes from 1-20 is 10.5. Modifiers then shift this average.

So if you have +4, the average roll will be 14.5, and if you have -5 your average roll will be 5.5.

We want that average to be above the AC of the creature we’re aiming for to make our attacks worth it. If we’re attacking with the penalty, then our modifiers have to be at least equal to the targets AC – 5.5. So for a target with 13 AC, we need to have a bonus of +8 (we can’t have 7.5 so we round up).

If you have advantage, the average roll of your dice goes up to 13.825, this is a bit more complicated to explain. Since you’re taking the higher roll, the chance that you’ll roll two 1s is incredibly low, almost 0%. On the other hand, the chance of one of the two dice rolls being a 20 goes up from 5% to almost 10%.

So, with advantage you can roughly say that our modifiers have to be at least equal to the target’s AC – 8.825 instead.

Then we just solve for the target’s AC to get the equations I put above.

Damage is where things get tricky. Let’s assume your average damage on a hit is 10 (2d4 + 5). If your attack modifiers add up to +6, your average attack roll for a normal attack becomes 16.5.

If the target’s AC is 17, your average damage is going to become 5, because you’re only hitting half the time (10/20 rolls of the d20 are lower than what you need to hit the 17).

If we’re taking the penalty to get a bonus 10 damage, the average damage actually stays the same. Since we’re dealing an average of 20 on a hit, but we’re now only hitting a quarter of the time, the average damage stays at 5. 

I would say we only want to take the penalty if we’re going to increase our damage. So we need to know our equation for great weapon master’s average damage and the equation for normal average damage. Then we’re going to set the inequality and solve for our target’s AC.

Essentially, the equations are the average weapon damage (AWD) multiplied by the percentage chance of you hitting the AC. The equations, which disregard critical damage, are as follows:

  • N (Normal average damage) = AWD * (0.05 * (21+ modifiers – AC)
  • GWM (average damage with bonus) = (AWD + 10) * (0.05 * (16 + modifiers – AC)
  • If GWM ≥ N then AC ≤ 16 + modifiers – 0.4*AWD

So! At the end of the day, we want to attack them if we think their AC is less than or equal to 16 plus our modifiers minus four-tenths of our average damage.

If we have advantage this damage calculation get’s a lot more complicated, instead of a consistent 5% chance of each number being rolled, each number actually gets more likely. There is only a 1 in 400 chance of rolling a one, whereas we have almost a ten percent chance of rolling a 20.

Fortunately, because of this, it’s a solid bet that you’ll be able to beat your opponents AC, even with the -5 penalty. Which means you’re basically guaranteed to get that bonus damage.

So we really don’t have to worry about a bunch of equations, we can just say that we’ll take the penalty if we have advantage.

Which Classes Should Take the Great Weapon Master feat?

Any class that can proficiently use heavy weapons can take this feat and benefit from it. Since heavy weapons are all martial weapons in RAW, you’ll need to be in a class that has proficiency in martial weapons, or somehow pick up that proficiency from another source.

Barbarians, fighters, paladins, and rangers are all classes that are proficient with all martial weapons. Additionally, the battle smith artificer and the death, tempest, twilight, and war domain clerics gain proficiency in martial weapons through their subclass.

Barbarians are one of the best options for this feat. Their reckless attack feature that they gain at 2nd level is a consistent way to gain advantage, even if it gives the next attack roll against them advantage as well.

Choosing to activate both of these features at the same time will more than likely result in some great bonus damage, and if you’re lucky, a critical hit and a bonus action attack.

Fighters and paladins get access to the” great weapon fighting”  fighting style. This ability let’s two-handed weapon wielders reroll 1s and 2s on attack rolls. Since most heavy weapons also have the two-handed property, these abilities overlap very well. 

My opinion of the best subclasses from each class that gets martial weapon proficiency for this feat (not best in general) are as follows:

Wild Magic Barbarian – The wild magic barbarian gets access to bolstering magic which can give them a d3 bonus to attack rolls. It’s not much, but aside from the barbarians’ general reckless attacks, this is the only way to offset the -5 penalty.

Battle Master Fighter – This subclass is the best at a lot of things, so it’s place here should be no surprise. A couple maneuvers benefit attack rolls, but the precision attack maneuver alone is a perfect fit.

It allows you to add your superiority die to an attack roll. Since both your maneuvers and this gamble attack are choices you can make when attacking, they pair excellently.

You can ensure that almost none of your attack rolls will receive any penalty.

Oath of Conquest – Their guiding strike gives them a +10 to their attack rolls. This is amazing at any time, and definitely offsets the penalty. Their invincible conqueror capstone also lets them get critical hits on 19s and 20s, an excellent way to get more of those bonus action attacks.

Hunter Conclave Ranger – While the ranger is probably the worst class for this feature, the hunter conclave at least gives you a whirlwind attack ability at 11th level which lets you attack as many creatures as you want within 5 ft. of you.

If you take the penalty on each attack when there’s a good amount of creatures surrounding you, you’re bound to hit one of them. It’s not the best, but it’s something.

Which Feats Pair Well With Great Weapon Master?

Polearm Master – Three of the specified weapons for polearm master, the glaive, halberd, and pike, all have the heavy property as well as the reach property.

Only the glaive and halberd can be used for the first part of the feature which allows you to make a bonus attack with the blunt end, but all three can be used to make wider opportunity attacks.

Lucky – If you really need the extra damage you’ll want a way to ensure that you can reroll your attack roll on a bad throw. Lucky always comes through.

Mounted Combatant – If you happen to have a mount, you can gain consistent advantage on any creature that is smaller than your mount. It’s crazy, but if you are on an elephant you can technically still make attacks on the surrounding 10 ft with a weapon that has the reach and heavy properties, as well as gaining advantage on any creature large or smaller since elephants are huge beasts. (DMs, I’m sorry)

Slasher/Piercer/Crusher – Any of the damage type feats are great to have for a weapon specialist. Most heavy weapons deal slashing damage, but all types are represented. Just choose the type that you want to focus on and you’re golden.

This is a great feat, and if you want to use heavy melee weapons it should be a definite grab as soon as you can get it. I hope you enjoy slashing and smashing with the biggest weapons you can find. As always, happy adventuring.