Fahrenheit to Celsius Converter

What Is Fahrenheit?

Fahrenheit (°F) is a temperature scale proposed by physicist Daniel Gabriel Fahrenheit in 1724. Water freezes at 32°F and boils at 212°F at standard atmospheric pressure — a span of 180 degrees.

Fahrenheit is the primary temperature scale in the United States for weather, cooking, medical records, and everyday use. It is also used informally in a few Caribbean nations and Liberia. The rest of the world uses Celsius.

Key reference points: 0°F = −17.8°C (very cold day), 32°F = 0°C (freezing), 72°F = 22.2°C (room temp), 98.6°F = 37°C (body temp), 212°F = 100°C (boiling).

What Is Celsius?

Celsius (°C), also called centigrade, is the temperature scale used by the International System of Units (SI) for everyday and scientific purposes. Water freezes at 0°C and boils at 100°C at standard atmospheric pressure — a clean span of 100 degrees.

Named after Swedish astronomer Anders Celsius (1742), this scale is used in virtually every country except the United States. Medical, scientific, and engineering contexts worldwide use Celsius (or its absolute equivalent, Kelvin).

Key reference points: −40°C = −40°F (scales intersect), 0°C = 32°F (freezing), 37°C = 98.6°F (body temp), 100°C = 212°F (boiling).

Fahrenheit to Celsius Formula

Unlike most unit conversions, temperature uses an offset formula, not simple multiplication:

°C = (°F − 32) × 5/9 exact

Or equivalently: °C = (°F − 32) ÷ 1.8

The "−32" accounts for the offset between the two scales' zero points. The "×5/9" accounts for the different degree sizes (180 Fahrenheit degrees span the same range as 100 Celsius degrees, so each °F = 5/9 of a °C).

Worked Example

Convert 98.6°F (normal body temperature) to Celsius:

1. Subtract 32: 98.6 − 32 = 66.6
2. Multiply by 5/9: 66.6 × 5/9 = 37.0°C

So normal human body temperature is exactly 37°C — one of the most important temperature equivalences in medicine.

Quick Estimation

For mental math, use: subtract 30, then divide by 2. This gives a rough estimate within a few degrees — good enough for weather and daily life.

• 72°F → (72−30) ÷ 2 = 21°C (exact: 22.2°C)
• 90°F → (90−30) ÷ 2 = 30°C (exact: 32.2°C)
• 50°F → (50−30) ÷ 2 = 10°C (exact: 10°C — perfect!)

The error grows at extreme temperatures, but for the 30–100°F range most people encounter, the shortcut works well.

Body Temperature Reference

Cooking Temperature Reference

Weather Reference

Why Does Fahrenheit Use 32 and 212?

Daniel Fahrenheit originally calibrated his scale using three reference points: 0°F was the coldest temperature he could create (a brine ice mixture), 32°F was the freezing point of water, and 96°F was meant to be body temperature. When the scale was later standardized to make the boiling point exactly 212°F, body temperature shifted slightly to 98.6°F. The resulting 180-degree span between freezing and boiling (212 − 32 = 180) is an accident of history, not design — unlike Celsius's clean 100-degree span.

When You Need This Conversion

• Medical and health: US thermometers read in °F; medical literature and international guidelines use °C. Knowing that 100.4°F = 38°C (the CDC fever threshold) is critical for parents, nurses, and travelers abroad using metric thermometers.
• Cooking with international recipes: American recipes use °F; European and most international cookbooks use °C. "Bake at 350°F" means 177°C — getting this wrong can ruin a dish or pose a fire hazard.
• Travel and weather: A forecast of 30°C means 86°F (hot); 10°C means 50°F (cool jacket weather). Americans abroad and international visitors to the US need instant conversion to dress and plan appropriately.
• Science and engineering: All scientific work uses Celsius (or Kelvin). US engineering data in °F must be converted for international collaboration, publication, and regulatory compliance.