C # Correct box selection based on quantity

I'm trying to create a function that will select the correct box based on the amount of content in the box.

Here are my cardboard boxes that have the amount of items they can contain.

SMALL_PASCAL = 300
BIG_PASCAL = 600
BABY_BOX = 1200
A485_1201 = 1800
A4140_1901 = 3000
A485 = 5000

And here is the method that will return CartonType.

/// 
/// Get the type of cardboard
/// 
/// 



/// 
[Test]



Private static CartonType GetCartonType (int qty)
{
yes <= 300)
     {
         return CartonType.SMALL_PASCAL;
     }
     else if (qty > 300 && quantity <= 600)
     {
         return CartonType.SMALL_PASCAL;
     }
     else if (qty > 600 && quantity <= 1200)
     {
         return CartonType.BABY_BOX;
     }
     else if (qty > 1200 && quantity <= 1800)
     {
         return CartonType.A485_1201;
     }
     else if (qty >1800 && quantity <= 3000)
{
returns CartonType.A4140_1901;
}
else // 5000 or more.
{
returns CartonType.A485;
}
}

Calling the method.

int qty = 1540;
Console.WriteLine (GetCartonType (qty));

Output: A485_1201

Is there a better way to achieve this instead of a Yes declaration?
I also thought that what would happen if the amount is 10,000? of what would require 2 A485.