How much meat equal to 3 ounces?

You're asking about the amount of meat equivalent to 3 ounces. That's already the measurement!

3 ounces is a weight measurement, and it's commonly used to measure portions of meat.

To give you a visual idea of what 3 ounces of meat looks like, it's about the size of a deck of cards.

If you're looking for a different way to measure meat, like in terms of volume, you'll need to provide more information.