Which of the following option is the correct formula to convert °C to °F?

Appeared in: Central Institute of Psychiatry - 9 July 2022

Explanation

The correct formula to convert Celsius to Fahrenheit is F = (C × 9/5) + 32.
This formula correctly scales the Celsius value by a factor of 1.8 (or 9/5) because a Celsius degree is larger than a Fahrenheit degree.
It then adds 32 to account for the different zero points on the scales, as water freezes at 0°C and 32°F.

Option A: This formula calculates the conversion from Fahrenheit to Celsius, which is the reverse of what the question asks.
Option B: This formula is mathematically incorrect for any standard temperature conversion. It incorrectly adds 32 within the parenthesis.
Option D: This formula uses the incorrect fraction for converting Fahrenheit to Celsius. The multiplier should be 5/9, not 9/5.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Temperature scale conversion from Celsius to Fahrenheit as background academic context rather than a clinical decision trigger.
Nurses must be proficient in converting temperatures as some facilities document in Celsius while patients may understand Fahrenheit, or vice-versa. Accurate conversion is vital for assessing fever and hypothermia.
Patient education often involves converting temperatures. For example, explaining to a parent that their child's fever of 39°C is 102.2°F helps them understand the severity.
What if? If a nurse incorrectly uses the F-to-C formula (Option A) to convert 40°C, they would calculate a value of 4.4°F instead of the correct 104°F, leading to a gross misinterpretation of a high fever.

How to Approach the Question

First, identify the goal of the question: to find the formula that converts Celsius TO Fahrenheit (C → F).
This means the final formula must be in the format 'F = ...'. Scan the options to see which ones fit this format.
Only Option C, 'F=C9/5+32', is structured to solve for F.
To confirm, recall the conversion logic: multiply the Celsius temperature by 9/5 (or 1.8) and then add 32.
Test with a known value. For 0°C, the formula gives F = (0 * 9/5) + 32 = 32°F, which is correct. This confirms Option C is the right answer.
Recognize that Option A is the formula for the reverse conversion (F → C), and the other options are mathematically incorrect.

Concept Tested & Keywords

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E6 Nursing Fundamentals Taylor p. 120-122

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