Here's how to convert -10 degrees Fahrenheit to Celsius:

Formula:

Celsius = (Fahrenheit - 32) * 5/9

Calculation:

1. Subtract 32 from the Fahrenheit temperature: -10 - 32 = -42

2. Multiply the result by 5/9: -42 * 5/9 = -23.33

Answer: -10 degrees Fahrenheit is equal to -23.33 degrees Celsius.