This is probably the mechanic that confuses newcomers to Hearts of Iron IV the most, and the one least clearly explained out there. Here it is, straight up.
What Combat Width Is
Every division you form occupies a "width" in battle, based on how many battalions it has and what type they are. Each province has a maximum combat width per side: if you throw in more divisions than fit, the extras sit in reserve waiting for room, not fighting.
The ideal width isn't a fixed number: it depends on terrain. A plain allows for much more combat width than mountains or forest, where the battle space is far narrower.
Recommended Combat Widths
Different community sources cite somewhat different values, and that's normal — they change with every major game patch. The classic values you'll see repeated are 10, 15, 18, 20, 27, 35 and 40-42.
What's consistent advice across every source:
- Avoid divisions under 10 width — they take a combat penalty for being too small.
- Aim for a minimum of around 30 organization points, so the front doesn't break on the first enemy offensive.
Two Templates to Start With
Instead of chasing "the perfect template" with external calculators, two clearly distinct basic templates are enough for your first games:
- Cheap shield: infantry (8-10 battalions) + engineers + support artillery, combat width ~15-18. Holds the front without spending expensive resources or military factory time.
- Expensive sword: tanks or special forces, combat width ~30. Used at the exact point where you want to break the enemy line, not across the whole front.
The logic is simple: cover kilometers of front cheaply with the shield, and concentrate the expensive spending (tanks, special equipment) only where you're actually going to attack.
A Note on Patches
Exact combat width values change with game updates. Any guide — this one included — should state which version it applies to, and it's worth double-checking after a major patch before trusting the numbers 100%.