What is a small size envelope called?

Standard Sizes: Number Envelope Size

5 W: 5.5H: 3.0625

6 W: 6H: 3.375

6 1/4 W: 6H: 3.5

6 1/2 W: 6.25H: 3.5625

6 3/4 W: 6.5H: 3.625

7 W: 6.75H: 3.75

7 1/2 W: 7.625H: 3.75

7 3/4 W: 7.5H: 3.875

Data Card W: 7.625H: 3.5

8 5/8 W: 8.625H: 3.625

9 W: 8.875H: 3.875

10 W: 9.5H: 4.125

10 1/2 W: 9.5H: 4.5

11 W: 10.375H: 4.5

12 W: 11H: 4.75

14 W: 11.5H: 5

So a 'Small Envelope' would be a 'Number 5 Envelope'