To convert Celsius to Fahrenheit, use the formula: (°C × 9/5) + 32. For 40°C: (40 × 9/5) + 32 = 72 + 32 = 104°F. So, 40°C equals 104 degrees Fahrenheit. This conversion is commonly applied in weather forecasts, science, and cooking measurements between the Celsius and Fahrenheit temperature scales.