To find the unit rate of chairs per row, you divide the total number of chairs by the total number of rows.
\[ \text{Chairs per row} = \frac{\text{Total chairs}}{\text{Total rows}} = \frac{920 \text{ chairs}}{46 \text{ rows}} \]
Calculating this gives:
\[ \frac{920}{46} = 20 \]
Thus, the unit rate is 20 chairs per row.