To convert temperatures from Celsius to Rankine, use the formula: °R = (°C × 9/5) + 491.67. This means you multiply the Celsius temperature by 1.8 and then add 491.67 to obtain the temperature in Rankine. For example, converting 25°C involves: (25 × 1.8) + 491.67 = 536.67°R. The Rankine scale, named after physicist William John Macquorn Rankine, is an absolute temperature scale like Kelvin but uses Fahrenheit-sized degrees. It's primarily used in engineering fields within the United States. Understanding this conversion is essential for professionals dealing with thermodynamic calculations where both Celsius and Rankine scales are applicable.