How to Convert Celsius to Fahrenheit (With Formula Examples)

Temperature conversion between Celsius and Fahrenheit is one of the most common unit conversions people encounter, particularly when travelling between the United States and the rest of the world, following international recipes, or reading scientific literature. The two scales were developed independently and use different zero points and different degree increments, which is why a simple 1-to-1 ratio does not apply.

The Celsius to Fahrenheit Formula

To convert a temperature from Celsius to Fahrenheit:

°F = (°C × 9/5) + 32

This can also be written as °F = (°C × 1.8) + 32. The multiplication by 9/5 (or 1.8) accounts for the difference in degree size between the two scales. Adding 32 accounts for the offset between their zero points — 0°C (the freezing point of water) corresponds to 32°F, not 0°F.

Worked Example: Converting 25°C

Step 1: 25 × 1.8 = 45Step 2: 45 + 32 = 77Result: 25°C = 77°F

The Fahrenheit to Celsius Formula

To convert from Fahrenheit back to Celsius, reverse the operations:

°C = (°F − 32) × 5/9

Worked Example: Converting 98.6°F

Step 1: 98.6 − 32 = 66.6Step 2: 66.6 × 5/9 = 66.6 × 0.5556 ≈ 37Result: 98.6°F = 37°C (normal body temperature)

Key Reference Points

These fixed temperature values are worth memorising for quick mental estimates:

• −40°C = −40°F — the one point where both scales intersect
• 0°C = 32°F — freezing point of water
• 20°C = 68°F — comfortable room temperature
• 37°C = 98.6°F — normal human body temperature
• 100°C = 212°F — boiling point of water at sea level

A Quick Mental Approximation

For everyday use, particularly when checking weather forecasts while travelling, a rough mental approximation works well: double the Celsius temperature and add 30. This gives an answer within 2–4 degrees for temperatures in the 0–40°C range, which covers most weather conditions.

Example: 22°C → (22 × 2) + 30 = 74°F. Exact answer: 71.6°F. Close enough for a weather check.

For precise conversions, especially in cooking or scientific contexts, use our free Unit Converter, which handles temperature alongside length, weight, and volume conversions.

Why the Two Scales Exist

Daniel Gabriel Fahrenheit proposed his scale in 1724, setting 0°F at the coldest temperature he could achieve with a brine mixture and 96°F at human body temperature. Anders Celsius introduced his scale in 1742, defining 0° as the boiling point of water and 100° as the freezing point — the reverse of the modern convention. After Celsius's death, the scale was inverted to the form we use today.

The Celsius scale was designed to align with natural physical reference points, making it easier to use in scientific contexts. Fahrenheit's finer-grained scale (180 degrees between freezing and boiling, versus 100 in Celsius) does offer slightly more precision when expressing common temperatures without decimal places, which is part of why it persisted in everyday American usage.

For a deeper look at all three major temperature scales and their scientific foundations, see our article on The Science Behind Temperature Scales.

Celsius to Fahrenheit Conversion Table

Frequently Asked Questions