Here's how to convert 91 degrees Fahrenheit (°F) to Celsius (°C):

Formula:

°C = (°F - 32) × 5/9

Calculation:

1. Subtract 32 from the Fahrenheit temperature: 91 - 32 = 59

2. Multiply the result by 5/9: 59 × 5/9 = 32.78

Therefore, 91 degrees Fahrenheit is approximately 32.78 degrees Celsius.