Arrays vs Lists in C#: Which One Should You Use In Unity?

TGIF! Welcome to another blog post about a question nearly every beginner Unity dev asks at some point: should this be an array or a List? And if you're absolutely new to coding, what is it exactly? If you've ever stared at an inventory system or a spawn pool wondering which one to reach for, you're in the right place. 

Let's go over this together!

The Core Concept Of Arrays And Lists

Both are ways to store multiple values in a single variable instead of creating a separate variable for every item. Got 10 enemies to track? You don't want enemy1, enemy2, all the way to enemy10. You want one collection holding all 10.

That's where arrays vs lists C# comes in as a genuine design decision, not just a syntax choice. Both do the same basic job, holding a group of values of the same type, but they behave differently under the hood, and that difference matters more than beginners usually expect.

collection  →  holds multiple values of the same type  →  accessed by index (0, 1, 2...)

Arrays: Fixed Size, Fast And Simple

An array is the most basic of the two. You declare its size up front, and that size never changes for the lifetime of that array.

int[] scores = new int[5];
scores[0] = 100;
scores[1] = 85;

string[] items = { "Sword", "Shield", "Potion" };
Debug.Log(items[0]); // "Sword"

Notice that second example, you can set every value right at creation using curly braces. Arrays are great when you know exactly how many items you'll ever need. A chessboard always has 64 squares. A week always has 7 days. In cases like that, an array is the right call, it's light on memory and fast to access.

The catch: try to add a 6th item to an array sized for 5, and you'll hit a runtime error. Arrays don't grow. If your game needs a collection that changes size while it's running, like pulling items into and out of an inventory, an array starts fighting you pretty quickly.

Lists: Flexible Size, Built For Change

A List<T> solves exactly that problem. It behaves like an array in most ways, same indexing, same idea of holding multiple values, but it can grow and shrink while your game is running.

List inventory = new List();
inventory.Add("Sword");
inventory.Add("Shield");
inventory.Remove("Sword");

Debug.Log(inventory[0]); // "Shield"
Debug.Log(inventory.Count); // 1

That Add and Remove flexibility is the entire reason List exists. Picking up a new weapon? inventory.Add(newWeapon). Dropping an item? inventory.Remove(item). No resizing logic to write yourself, the List handles it internally.

Also notice Count instead of Length, that's a small but common gotcha. Arrays use .Length, Lists use .Count. Mix them up and you'll get a compiler error reminding you pretty quickly.

Arrays Versus Lists In Unity: Where Each One Actually Shines

This is the part that actually matters day to day. Here's how it breaks down in real Unity projects:

• Fixed set of spawn points - you know exactly how many spawn points exist in a level and that number never changes mid-game. Array.
• Player inventory - items get added and removed constantly as the player plays. List.
• Days of the week for a schedule system - always exactly 7. Array.
• Active enemies currently alive in a wave - enemies spawn in, die, get removed. List.
• A fixed set of difficulty settings (Easy, Medium, Hard) - never changes at runtime. Array.
• Projectiles currently in flight - new ones created, old ones destroyed constantly. List.

Notice the pattern in that arrays vs lists Unity comparison: if the collection's size is locked in and known ahead of time, reach for an array. If it changes while the game runs, reach for a List.

Looping Through Both

Good news, looping works almost identically for both, which is part of why beginners sometimes don't notice the difference at first:

string[] weapons = { "Sword", "Bow", "Staff" };
foreach (string weapon in weapons)
{
    Debug.Log(weapon);
}

List potions = new List { "Health", "Mana", "Speed" };
foreach (string potion in potions)
{
    Debug.Log(potion);
}

foreach doesn't care whether it's walking through an array or a List, it just visits each item in order. A regular for loop works the same way too, just swap .Length for .Count depending on which collection you're using.

Performance: Does It Actually Matter?

For most solo dev projects, honestly, no, not enough to obsess over. Arrays are marginally faster and use slightly less memory since they don't carry the overhead a List needs to manage its resizing. But unless you're iterating over tens of thousands of items every single frame, the difference is not something you'll notice in a typical game.

The real deciding factor in the arrays vs lists C# debate almost always comes down to whether your collection's size needs to change, not raw performance. Pick based on that first. Optimize later, if you ever actually need to.

So Which One Should You Actually Use?

Here's the no-fluff version, the gut check you can run through in your head:

• Size never changes, known ahead of time → array
• Size changes while the game runs → List<T>
• Need .Add() or .Remove() → List<T>, arrays can't do this
• Squeezing out every last bit of performance in a hot loop → array
• Not sure yet → start with List<T>, it's more forgiving while you're prototyping

Picking the right collection in the arrays vs lists Unity decision isn't about which one is "better," it's about asking "does this collection's size ever change while the game is running?" Answer that honestly and the right choice picks itself almost every time.

Wrapping Up

Arrays and Lists solve the same basic problem, storing multiple values together, but they solve it differently enough that picking the wrong one causes real friction down the line. Default to a fixed-size array when you know your count up front, reach for a List the moment that count needs to change, and you'll avoid most of the headaches beginners run into with collections. 

 ~happy Coding!