Temperature in Celsius:
Table of Contents
Fahrenheit to Celsius, converted instantly
Enter any temperature in Fahrenheit and this calculator returns the exact Celsius equivalent using °C = (°F − 32) × 5/9. Use it for weather forecasts, cooking temperatures, body temperature checks, scientific conversions, and travel planning between imperial and metric countries.
The formula
To convert a Fahrenheit temperature to Celsius, subtract 32 then multiply by 5/9:
°C = (°F − 32) × 5/9
- °C — the temperature in degrees Celsius (result).
- °F — the temperature in degrees Fahrenheit (input).
- −32 — removes Fahrenheit’s zero offset (Fahrenheit’s zero is not the same reference as Celsius’s).
- 5/9 — the ratio of a Celsius degree to a Fahrenheit degree (equivalently, divide by 1.8).
An equivalent form: °C = (°F − 32) / 1.8.
Worked example
Using the calculator’s default of 80°F:
- Subtract 32: 80 − 32 = 48.
- Multiply by 5/9: 48 × 5/9 = 240/9 = 26.67°C.
So 80°F = 26.67°C — a warm summer afternoon.
Fahrenheit to Celsius reference table
Key reference temperatures across both scales:
| °F | °C | Notable point |
|---|---|---|
| −459.67 | −273.15 | Absolute zero (0 K) |
| −40 | −40 | Scales are equal |
| 0 | −17.78 | Very cold winter |
| 32 | 0 | Water freezes (1 atm) |
| 50 | 10 | Cool spring day |
| 68 | 20 | Comfortable room temperature |
| 77 | 25 | Warm room / mild summer |
| 86 | 30 | Hot summer day |
| 98.6 | 37 | Human body temperature (Wunderlich 1868) |
| 212 | 100 | Water boils (1 atm) |
History & standards
Daniel Gabriel Fahrenheit (1724) set his zero at the freezing point of a saturated salt-water brine (the coldest reproducible temperature he could make in his lab), placed 96 at human body temperature, and found that pure water froze at 32°F and boiled at 212°F — a range of exactly 180 degrees. After his death the body-temperature point was recalibrated to 98.6°F so that the scale intervals aligned perfectly.
Anders Celsius (1742) originally defined his scale with 0 at the boiling point of water and 100 at the freezing point — the opposite of today’s convention. After Celsius’s death in 1744, botanist Carl Linnaeus and astronomer Mårten Strömer inverted the scale to its modern form (0 = freezing, 100 = boiling), which became the international standard.
Kelvin is the SI base unit for thermodynamic temperature. One kelvin equals one Celsius degree in size, but starts at absolute zero (0 K = −273.15°C = −459.67°F), where all thermal motion ceases. Scientific work uses Kelvin because it eliminates negative values in thermodynamic equations.
Common applications
- Weather. Most of the world reports weather in °C; the US uses °F. A US forecast of 95°F is 35°C — a heat-wave threshold in many countries. Understanding the conversion matters when travelling or following international news.
- Cooking. American recipes specify oven temperatures in °F. A 350°F moderate oven is 176.7°C; 400°F is 204.4°C. Meat safety guidelines (e.g. 165°F / 73.9°C for poultry) also use °F in US sources.
- Body temperature. Normal resting temperature is ~37°C / 98.6°F. A fever is generally defined as ≥38°C / 100.4°F by most clinical guidelines.
- Scientific work. Laboratory temperatures are stated in °C (or Kelvin) worldwide. Reaction rates, solubility curves, and gas laws all reference Celsius or Kelvin rather than Fahrenheit.
Reverse conversion
To go the other way — Celsius back to Fahrenheit — multiply by 9/5 then add 32:
°F = (°C × 9/5) + 32
Use our Celsius to Fahrenheit calculator for instant reverse conversions.
Useful facts & limits
- The −40 trick. −40°F = −40°C exactly — the only point where both scales agree. Plug it in: (−40 − 32) × 5/9 = −72 × 5/9 = −40.
- Degree size. One Celsius degree is 1.8 times larger than one Fahrenheit degree. A 1°F change equals a 0.556°C change.
- Absolute zero. Temperature cannot go below 0 K = −273.15°C = −459.67°F. This is the theoretical floor of thermodynamic temperature.
- Boiling depends on pressure. Water boils at 100°C (212°F) only at standard sea-level pressure (101.325 kPa). At altitude, the boiling point drops.
- Quick mental estimate. For a rough conversion in your head: subtract 30 from the Fahrenheit value and divide by 2 (e.g. 80°F → 50/2 = 25°C vs. the exact 26.67°C). Accurate to within a few degrees for everyday temperatures.
Sources & references
- NIST, “Kelvin (SI base unit).” physics.nist.gov.
- Britannica, “Daniel Gabriel Fahrenheit.” Encyclopaedia Britannica.
- Britannica, “Anders Celsius.” Encyclopaedia Britannica.
FAQs
−40° is the one temperature where both scales agree exactly. At −40°F the Celsius formula gives (−40 − 32) × 5/9 = −72 × 5/9 = −40°C. This crossover is a useful mental anchor: above −40 the Fahrenheit reading is always numerically higher than Celsius; below −40 the Fahrenheit reading is lower.
Daniel Gabriel Fahrenheit set his zero in 1724 at the freezing point of a saturated brine solution (ice, water, and ammonium chloride), the coldest reproducible temperature he could achieve in the lab. He then placed the human body temperature at 96°F and found that pure water froze at 32°F and boiled at 212°F — a span of exactly 180 degrees, divisible by many small integers, which Fahrenheit considered a practical advantage.
The classic reference is 37°C (98.6°F), derived from Carl Wunderlich’s 1868 survey of over a million axillary readings. Modern population studies (e.g. Protsiv et al., eLife 2020) suggest the true average is closer to 36.6°C (97.9°F) and has been declining slowly since the 19th century. A reading between 36.1°C and 37.2°C (97–99°F) is generally considered normal for a resting adult.
The US adopted the Fahrenheit scale in the colonial era and, unlike most other countries, never completed a switch to Celsius. Everyday weather in Fahrenheit maps neatly to a 0–100 range for typical human experience (0°F is extremely cold; 100°F is very hot), which many Americans find intuitive. Metrication efforts in the 1970s stalled, leaving Fahrenheit entrenched in infrastructure, education, and public habit.
Scientists use Kelvin (K), the SI base unit for thermodynamic temperature. One kelvin equals one Celsius degree in size, but the Kelvin scale starts at absolute zero — the point at which all thermal motion ceases. Absolute zero is 0 K = −273.15°C = −459.67°F. Using Kelvin avoids negative numbers in thermodynamic equations and is required for laws such as the ideal gas law PV = nRT.
Only at standard atmospheric pressure (101.325 kPa / 1 atm). At higher altitudes where air pressure is lower, water boils below 100°C — at 5,000 m (about 16,400 ft) it boils at roughly 83°C (181°F). In a pressure cooker (above 1 atm) water can exceed 100°C in liquid form. The “100°C = boiling” rule is therefore a sea-level approximation.