Fahrenheit to Celsius Converter

The Fahrenheit to Celsius Formula

The conversion from Fahrenheit to Celsius uses the formula:

C = (F − 32) × 5/9

You subtract 32 because the two scales have different zero points: Celsius sets 0 at the freezing point of water, while Fahrenheit sets 32 at the same point. You then multiply by 5/9 (approximately 0.5556) to account for the different size of each degree. A Fahrenheit degree is smaller than a Celsius degree: there are 180 Fahrenheit degrees between freezing and boiling, but only 100 Celsius degrees.

Why Two Temperature Scales?

The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in 1724. He calibrated his scale using three fixed points: a brine freezing mixture (0°F), the freezing point of water (32°F), and human body temperature (originally 96°F, later refined to 98.6°F). The Celsius scale (originally called Centigrade) was proposed by Anders Celsius in 1742, using the more intuitive reference points of 0°C for water freezing and 100°C for water boiling at sea level.

Most of the world, including New Zealand, uses Celsius as the everyday temperature scale. The United States, a handful of Caribbean territories, and the Cayman Islands continue to use Fahrenheit for everyday purposes. Both scales are used in science; Kelvin (which shares the degree size of Celsius but starts at absolute zero) is the SI unit for thermodynamic temperature.

Worked Example (matches the default)

Converting 72°F (a comfortable room temperature) to Celsius:

1. Subtract 32: 72 − 32 = 40
2. Multiply by 5/9: 40 × 5 = 200, then 200 ÷ 9 = 22.22...
3. Result: 22.22°C (rounded to two decimal places)

To also get Kelvin, add 273.15 to the Celsius value: 22.22 + 273.15 = 295.37 K.

Quick Mental Approximation

For a rough conversion in your head, use this shortcut: subtract 30, then halve the result. For example, 70°F becomes (70 − 30) / 2 = 20°C. This is slightly off (actual answer is 21.1°C) but useful for quick estimates when you do not have a calculator handy.

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Method: Standard international conversion formula C = (F − 32) × 5/9, as defined by the International Temperature Scale. The relationship between Fahrenheit and Celsius is exact and does not require periodic updates. Kelvin conversion uses K = C + 273.15 (BIPM, SI Brochure 9th edition). Rankine: R = F + 459.67.

This converter applies the exact mathematical formula and does not round inputs before calculation. Results are displayed to two decimal places. For scientific applications requiring more decimal places, use the formula directly.