I put their number at around 20.

4 seconds sound clip from the 300 movie soundboard.

You can hear this line at 00:30:19 in the Blu-ray version of the movie.

Quote context

[...]

- We're being followed.

- It has followed us since Sparta.

- My king! Look!

- What happened here? Where are all the people?

- Persians.

- I put their number at around 20.

- A scouting party.

- But these footprints...

- Behind us!

- Child!

[...]