Fahrenheit to Celsius
°F
°C
Conversion History
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Quick Reference Table (Fahrenheit to Celsius)
| Fahrenheit (°F) | Celsius (°C) |
|---|---|
| -40 | -40 |
| 32 | 0 |
| 68 | 20 |
| 98.6 | 37 |
| 212 | 100 |
About Fahrenheit (°F)
Fahrenheit (°F) is the temperature scale used in the United States for everyday measurements such as weather, cooking, and body temperature. The scale was proposed by German physicist Daniel Gabriel Fahrenheit in 1724. Its original reference points included the freezing point of a salt-water brine (0°F) and normal human body temperature (approximately 96°F in his calibration). Water freezes at 32°F and boils at 212°F at standard pressure — a 180-degree span, compared to 100 degrees in Celsius. Each Fahrenheit degree is therefore 5/9 of a Celsius degree. Fahrenheit remains the primary scale for US weather forecasts, oven temperatures, and thermostats.
Water freezes at 32°F and boils at 212°F. A hot summer day in the US is around 95°F; normal body temperature is 98.6°F.
Etymology: Named after Daniel Gabriel Fahrenheit (1686–1736), a German physicist and instrument maker based in Amsterdam. He invented the mercury-in-glass thermometer and proposed the scale in 1724. His zero was set at the lowest temperature he could reliably reproduce using a salt-ice mixture.
About Celsius (°C)
Celsius (°C) is the most widely used temperature scale in the world, adopted by every country except the United States, Liberia, and Myanmar for everyday and scientific use. Zero degrees Celsius is defined as the freezing point of water at standard atmospheric pressure; 100°C is the boiling point. Originally called centigrade because of its 100-degree span between these two reference points, it was renamed Celsius in 1948 to honor Swedish astronomer Anders Celsius. It is the practical temperature scale for weather, cooking, medicine, and most scientific work outside thermodynamics. Body temperature is 37°C; a comfortable room is typically 20–22°C.
Water freezes at 0°C and boils at 100°C. Normal human body temperature is 37°C. A warm summer day in southern Europe is around 35°C.
Etymology: Named after Swedish astronomer Anders Celsius (1701–1744), who proposed a 100-degree scale in 1742. His original scale was inverted — 0°C meant boiling, 100°C meant freezing — and was reversed by fellow Swede Carl Linnaeus shortly after his death.
Fahrenheit – Frequently Asked Questions
Why does the US use Fahrenheit instead of Celsius?
The United States adopted Fahrenheit in the colonial era when it was the dominant scientific scale. When the metric system spread through Europe in the late 18th and 19th centuries, the US did not follow. Multiple metrication attempts (notably in the 1970s) failed to gain public support, leaving Fahrenheit entrenched in daily life and infrastructure.
At what temperature are Fahrenheit and Celsius the same?
Fahrenheit and Celsius are equal at −40°. At that point −40°C = −40°F. This is the only temperature where the two scales intersect, arising naturally from the conversion formula: °F = °C × 1.8 + 32, which equals °C only when both sides solve to −40.
Why does Fahrenheit use 32 for freezing instead of 0?
Fahrenheit set his 0°F at the coldest temperature he could reliably reproduce — a salt-ice-water brine — so that everyday weather readings would never go negative in temperate Europe. Water's freezing point landed at 32°F and body temperature at 96°F (later corrected to 98.6°F). The seemingly odd number 32 is simply where water freezing fell on his scale after he anchored zero to the brine. The 32-to-212 span (180 degrees) also divides neatly by many factors, which suited 18th-century instrument makers.
What Fahrenheit temperature is considered dangerously hot for humans?
Internal body temperature above 104°F (40°C) is heat stroke territory — a medical emergency. Externally, a wet-bulb temperature of 95°F (35°C) is the theoretical limit of human survival because the body can no longer cool itself by sweating. Air temperatures above 130°F (54°C) have been recorded in Death Valley, but low humidity keeps wet-bulb values survivable there. In humid climates, even 110°F (43°C) air temperature can be lethal because moisture prevents sweat evaporation.
Why is body temperature 98.6°F and not a round number?
98.6°F is the Fahrenheit equivalent of 37°C, which is itself a rounded metric value. Fahrenheit introduced his scale before Celsius, so 37°C converting to a non-round Fahrenheit value is an artifact of the conversion arithmetic. In practice, normal body temperature varies from about 97°F to 99°F (36.1–37.2°C) across individuals and times of day.
Celsius – Frequently Asked Questions
Which countries use Celsius?
Almost every country in the world uses Celsius for everyday temperatures — weather forecasts, cooking, and body temperature. The United States, Liberia, and Myanmar are the principal exceptions, using Fahrenheit for daily life, though US scientists use Celsius for research.
What is absolute zero in Celsius?
Absolute zero — the theoretical minimum temperature where molecular motion effectively ceases — is −273.15°C. This corresponds to 0 K on the kelvin scale. It is not physically achievable but has been approached to within a few billionths of a degree in laboratory conditions.
How do you convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (or 1.8) and add 32. For example, 20°C × 1.8 + 32 = 68°F. A quick mental approximation: double the Celsius value and add 30 (gives ±2°F accuracy for typical weather temperatures).
What is normal body temperature in Celsius?
Normal human body temperature is approximately 37.0°C (98.6°F), though it varies by individual, time of day, and measurement site. A temperature above 38.0°C is generally considered a fever; hypothermia is diagnosed below 35.0°C.
What is the difference between Celsius and centigrade?
Centigrade is the old name for the same scale — both refer to a 100-degree span between water's freezing and boiling points ("centi" = 100, "grade" = step). The name was officially changed to Celsius in 1948 to avoid confusion with the angular unit also called "grade" (or "gradian") in some languages.