40k Damage Calculator

A 40k damage calculator helps you estimate how much damage an attack is likely to do before you commit a unit to shooting or melee. Instead of guessing, you can check your expected hits, wounds, failed saves, and final damage in one place. That makes it easier to choose targets, compare weapons, and avoid wasting attacks.

For Warhammer 40k players, this kind of tool is basically a fast Mathhammer calculator. It takes the core attack sequence and turns it into a practical number you can use during list building or while planning a turn. In the current core rules, attacks still follow the familiar flow of hit roll, wound roll, saving throw, and damage, so a calculator built around that flow is useful for both casual and competitive play.

What Is a 40k Damage Calculator?

A Warhammer 40k damage calculator is a tool that estimates the average damage output of a weapon or unit against a target. You enter the attack stats, the target’s defenses, and any rules that change the math. The calculator then gives you an expected result instead of leaving you to work everything out by hand.

That result is not a guaranteed outcome for one roll. It is an average over many possible outcomes. This matters because good decisions in 40k are rarely about chasing the perfect spike. They are about knowing what your unit will usually do, not what it might do once on a lucky turn.

How to Use the 40k Damage Calculator

Using the calculator should be simple if you already have the weapon profile and target profile in front of you.

Enter attacks and hit chance

Start with the number of attacks. Then enter the unit’s Ballistic Skill for shooting or Weapon Skill for melee. This tells the tool how likely the attack is to hit.

Add Strength, Toughness, AP, and saves

Next, enter the weapon’s Strength and the target’s Toughness. That comparison determines the wound roll. After that, add the weapon’s AP and the target’s save characteristic. If the target has an invulnerable save, use whichever save is actually relevant for that attack. The current rules still center damage resolution around Strength, Toughness, AP, saves, and damage, so these are the most important inputs in the tool.

Include damage and special rules

Finally, enter the weapon’s damage. For flat damage, this is easy. For variable damage like D3 or D6, use the average value unless your tool already handles dice averages automatically.

You should also include any special rules that materially change output. In current 40k rules language, keywords like Blast, Devastating Wounds, Lethal Hits, and Sustained Hits can noticeably change expected damage, so they should not be ignored.

How 40k Damage Is Calculated

At its simplest, the logic behind a 40k damage calculator looks like this:

Expected Damage = Attacks × Hit Chance × Wound Chance × Failed Save Chance × Average Damage

That formula gives you a good baseline. From there, the tool adjusts the number when special rules, rerolls, or bonus hits change the normal flow.

For example, a weapon that hits on 3+ has a hit chance of 2/3. A weapon that wounds on 4+ has a wound chance of 1/2. If the target fails its save half the time and each failed save deals 2 damage, you multiply all of those steps together to estimate the average result.

Why Strength vs Toughness Matters

One of the biggest drivers of damage in 40k is the relationship between Strength and Toughness. That comparison tells you how hard it is to convert a hit into a wound. In practical terms, this is often the first thing players should check when comparing weapons against different targets.

A gun that looks strong on paper can underperform badly into the wrong target profile. On the other hand, a weapon with a better Strength breakpoint can outperform a weapon with higher raw damage because it simply wounds more often. That is exactly why a 40k damage calculator is useful. It helps you compare real output instead of trusting first impressions.

How AP and Saves Affect the Result

After a successful wound roll, the defender gets a saving throw unless a rule changes that step. This is where AP becomes very important. Higher AP makes armour saves worse, which increases the chance that damage goes through.

Invulnerable saves can change the math again. A target may ignore your modified armour save calculation and rely on its invulnerable save instead. That is why it is important to test both high-AP and lower-AP weapons against elite targets before assuming which one is best.

Special Rules That Change Damage Output

Some rules do much more than add a small bonus. They can change the shape of the calculation itself.

Blast

Blast increases the number of attacks against larger units. In the current quick-start rules, it adds 1 attack for every five models in the target unit, rounding down. That means a weapon can become much more efficient into squads than its basic profile suggests.

Lethal Hits and Sustained Hits

Lethal Hits can turn critical hits into automatic wounds, while Sustained Hits creates extra hits on critical hits. These two rules do different jobs. Lethal Hits is often more valuable when your Strength is low into a tough target. Sustained Hits is often better when you already have a good chance to wound and simply want more volume.

Devastating Wounds

Devastating Wounds is another major damage rule. In the quick-start guide and related core rules materials, a Critical Wound with Devastating Wounds inflicts mortal wounds equal to the weapon’s damage instead of normal damage. That can dramatically change expected output against well-armoured targets.

Example 40k Damage Calculation

Here is a simple example using clean numbers.

Let’s say a weapon makes 3 attacks, hits on 3+, wounds on 3+, pushes the target to a failed save chance of 2/3, and deals 2 damage per failed save.

Now work through the math:

• Attacks: 3
• Hit chance: 2/3
• Wound chance: 2/3
• Failed save chance: 2/3
• Damage: 2

Expected damage:

3 × 2/3 × 2/3 × 2/3 × 2 = about 1.78 damage

That does not mean the weapon will always deal 1.78 damage in a real game. It means that, on average, this is the kind of output you should expect over time. That is the real value of Mathhammer.

How to Read the Result

The most useful way to read the result is as a planning tool.

If one unit only averages a small amount of damage into a target, you may need support from another unit. If a weapon’s expected damage is much lower than you assumed, you can change target priority before wasting an activation. If two weapons look similar, the calculator can show which one is actually more efficient into a specific profile.

This is also helpful for avoiding overkill. You do not always need to throw your heaviest anti-tank gun into a half-dead unit. A good damage calculator helps you estimate the minimum firepower needed so you can use the rest of your army elsewhere.

A Better Way to Use This Tool

The best way to use a Warhammer 40k damage calculator is to compare real matchups, not just raw statlines in isolation.

Test your anti-infantry weapons into light infantry and elite infantry. Test your anti-tank weapons into vehicles and monsters. Run the same weapon into several targets and compare how much Strength breakpoints, AP, and special rules change the output.

Also make sure you enter the current datasheet values and current rules wording from the app, codex, or latest official updates. Games Workshop continues to publish rules commentary and balance updates, so an accurate calculator depends on accurate inputs.

Frequently Asked Questions

What does a 40k damage calculator actually show?

It usually shows expected hits, expected wounds, failed saves, and average damage. Some tools also break down the full attack sequence so you can see where the damage is being lost.

Is this the same as a Mathhammer calculator?

Yes. “Mathhammer” is just the common term players use for probability-based analysis in Warhammer 40k. A 40k damage calculator is one of the most practical Mathhammer tools.

Does the calculator work for both shooting and melee?

Yes, as long as the tool lets you enter the correct WS or BS, Strength, AP, damage, and any special rules. The basic idea is the same in both cases.

How do invulnerable saves affect the result?

Invulnerable saves can cap how much value you get from AP. That means a very high-AP weapon is not always as efficient as it first looks when the target has a strong invulnerable save.

Should I use average damage for D3 and D6 weapons?

Yes, in most planning situations. A D3 averages 2, and a D6 averages 3.5. That gives you a much more reliable planning number than assuming a best-case roll.

Can I use this tool for list building?

Yes. It is useful both at the table and before the game. You can compare weapon options, evaluate unit roles, and check whether your list has enough reliable damage into the target types you expect to face.