C# Tip: Should You Use .ToList() or .ToArray()?

#csharp #programming #beginners #dotnet

It’s not just a matter of taste — your choice should depend on how the collection is consumed.

When working with LINQ in C#, you’ve probably called .ToList() or .ToArray() to materialize a query. But which one should you use?

var items = source.Where(x => x.IsValid).ToList();
// or
var items = source.Where(x => x.IsValid).ToArray();

Simple rule is:

Use .ToList() if the consumer will modify the collection (add/remove items).
Use .ToArray() if the consumer will only read or mutate existing values without changing the collection size.

For collections around 10,000 items or more , .ToList() is actually slightly faster than .ToArray(), this has been observed in benchmarks!

However, in .NET 9, performance updates optimized .ToArray(), making it more efficient for large datasets.

Recommendation

Don’t just default to one or the other. Think about: