To find the length of one side of a square when given the area, you can use the formula for the area of a square:
\[ \text{Area} = \text{side}^2 \]
Given that the area is 9 square feet, we can set up the equation:
\[ \text{side}^2 = 9 \]
To find the length of one side, take the square root of both sides:
\[ \text{side} = \sqrt{9} = 3 \text{ ft} \]
Now, to convert feet to inches, we use the conversion factor that 1 foot = 12 inches. Therefore:
\[ \text{side} = 3 \text{ ft} \times 12 \text{ inches/ft} = 36 \text{ inches} \]
Thus, the length of one side of the painting in inches is 36 inches.