There is a common estimation that one level tablespoon of baby formula powder equals 5 grams. Based on this estimation, 8.9 grams of baby formula powder would be equivalent to approximately 1.78 teaspoons.

However, it's essential to note that different baby formula brands may have varying densities and weights, and the provided estimation may not be precise. It's recommended to consult the specific instructions or measurements provided by the baby formula manufacturer to ensure accuracy.