Convert Fahrenheit to Celsius
This converter calculates the exact temperature equivalent between Fahrenheit (°F) and Celsius (°C), the two most widely used temperature scales in everyday life. The core formula for converting Fahrenheit to Celsius is °C = (°F − 32) × 5/9, while the reverse is °F = (°C × 9/5) + 32. Use this tool whenever you need to interpret a weather forecast, follow a recipe from another country, read a medical thermometer, or set an oven calibrated in a different unit. The Fahrenheit scale is standard in the United States, while Celsius is used by virtually every other country and all scientific disciplines worldwide.
When to use this calculator
- Reading a foreign weather forecast — a European city reporting 28 °C converts to 82.4 °F so you know to pack light summer clothes.
- Cooking with international recipes — a UK recipe calling for 180 °C oven temperature equals 356 °F on a US oven dial.
- Interpreting medical readings — a doctor abroad says a patient has 38.5 °C fever, which is 101.3 °F, signaling a moderate fever.
- HVAC and thermostat calibration — converting a recommended room comfort range of 68–72 °F to 20–22.2 °C for a smart thermostat set in Celsius.
- Food safety compliance — USDA guidelines state that poultry must reach 165 °F internally, equivalent to 73.9 °C, a critical threshold for safe cooking.
- Scientific lab work — converting ambient lab temperature specifications written in Celsius to Fahrenheit for US-manufactured equipment.
- Travel and outdoor planning — a NOAA forecast of 14 °F wind-chill in Montana equals −10 °C, warning of serious frostbite risk within 30 minutes.
Calculation Example
- Typical Value
- Result
How it works
3 min readHow It's Calculated
The two conversion formulas are exact — no rounding is introduced by the math itself:
Fahrenheit → Celsius: °C = (°F − 32) × (5 / 9)
Celsius → Fahrenheit: °F = (°C × 9 / 5) + 32Why subtract 32 first? The Fahrenheit scale sets water's freezing point at 32 °F rather than 0 °F, so you must remove that offset before scaling. The factor 5/9 (≈ 0.5556) accounts for the difference in degree size: one Celsius degree spans 1.8 Fahrenheit degrees.
Quick mental shortcut: Double the Celsius value and add 30 to get an approximate Fahrenheit reading (e.g., 20 °C → 40 + 30 = 70 °F; exact answer: 68 °F). Accurate to within ±2 °F for typical weather temperatures.
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Reference Table
| Fahrenheit (°F) | Celsius (°C) | Landmark Meaning |
|---|---|---|
| −459.67 | −273.15 | Absolute zero (0 K) |
| −40 | −40 | Scales intersect — identical value |
| 0 | −17.78 | Extremely cold winter day |
| 32 | 0 | Water freezes (sea level) |
| 50 | 10 | Cool spring morning |
| 68 | 20 | Comfortable room temperature |
| 77 | 25 | Warm indoor comfort zone |
| 98.6 | 37 | Normal human body temperature |
| 100 | 37.78 | Slightly above normal body temp |
| 104 | 40 | High fever threshold (seek care) |
| 140 | 60 | Minimum safe temp for fish (USDA) |
| 165 | 73.89 | Safe internal temp for poultry (USDA) |
| 212 | 100 | Water boils (sea level) |
| 350 | 176.67 | Typical baking temperature |
| 451 | 232.78 | Paper ignition point |
| 1,832 | 1,000 | Threshold for many industrial furnaces |
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Typical Examples
Example 1 — Weather:
A Paris weather app shows 22 °C. Is it warm enough for shorts?°F = (22 × 9/5) + 32 = 39.6 + 32 = <strong>71.6 °F</strong> — Yes, pleasantly warm.
Example 2 — Cooking:
A Spanish recipe requires a 200 °C oven. Your US oven uses °F.°F = (200 × 9/5) + 32 = 360 + 32 = <strong>392 °F</strong> — Set the dial to 392 °F (or 400 °F in practice).
Example 3 — Medical:
A child's temperature reads 103 °F. A grandparent abroad asks the equivalent.°C = (103 − 32) × 5/9 = 71 × 0.5556 = <strong>39.4 °C</strong> — This is a significant fever; the CDC recommends contacting a healthcare provider at ≥39 °C (102.2 °F) in children.
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Common Mistakes
1. Forgetting to subtract 32 before multiplying — The most frequent error. Doing °F × 5/9 without removing the 32-degree offset gives a completely wrong result (e.g., 100 °F incorrectly becomes 55.6 °C instead of the correct 37.8 °C).
2. Inverting the fraction (using 9/5 instead of 5/9 in F→C) — Using the wrong direction of the factor flips the scale. Always use 5/9 when converting to Celsius and 9/5 when converting to Fahrenheit.
3. Rounding too early in a chain calculation — If you round 5/9 to 0.56 at the first step, errors compound. Use the full fraction or at least 4 decimal places (0.5556) for medical or scientific work.
4. Confusing Celsius with Kelvin in scientific contexts — Celsius and Kelvin share the same degree size, but 0 °C = 273.15 K. If a chemistry formula requires Kelvin, add 273.15 to your Celsius result; do not plug in Fahrenheit directly.
5. Assuming −40 is always a trick question — −40 °F = −40 °C exactly. This is the only point where both scales share the same numerical value, useful as a mental anchor.
6. Using the "double and add 30" shortcut for extreme temperatures — This approximation works well between −10 °C and 40 °C. Outside that range (e.g., oven temperatures or sub-zero arctic conditions), the error exceeds 5 °F and you must use the exact formula.
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Frequently asked questions
What is the exact formula to convert Fahrenheit to Celsius?
The exact formula is °C = (°F − 32) × 5/9. No approximation is involved — the relationship between the two scales is a fixed linear equation. For example, 77 °F gives (77 − 32) × 5/9 = 45 × 0.5556 = 25 °C exactly.
At what temperature are Fahrenheit and Celsius the same number?
The two scales meet at exactly −40 degrees — that is, −40 °F = −40 °C. You can verify it with either formula: (−40 − 32) × 5/9 = −72 × 0.5556 = −40 °C. This is the only point where both scales share the same numerical value and it commonly appears in arctic weather reporting.
What is normal human body temperature in both scales?
The long-established clinical standard is 98.6 °F = 37.0 °C. However, a 2020 study from the Stanford University School of Medicine (published in eLife) found the modern average is closer to 97.9 °F (36.6 °C), reflecting changes in chronic inflammation and environmental conditions over the past 150 years. The CDC still uses 100.4 °F (38 °C) as the clinical fever threshold.
What temperatures does the USDA consider safe for cooking meat?
The USDA Food Safety and Inspection Service specifies minimum internal cooking temperatures: 145 °F (62.8 °C) for whole cuts of beef, pork, veal, and lamb (with a 3-minute rest); 160 °F (71.1 °C) for ground meats; and 165 °F (73.9 °C) for all poultry, stuffing, and leftovers. These thresholds are set to destroy Salmonella, E. coli O157:H7, and other pathogens.
How does NOAA use temperature scales in its forecasts?
NOAA's National Weather Service publishes all public forecasts in Fahrenheit for US domestic audiences, while its scientific datasets and international bulletins use Celsius. NOAA's Climate Reference Network records temperatures to 0.1 °C precision. Wind chill and heat index values — both calculated from °F in US public forecasts — are also available in °C through NOAA's API for developers building international apps.
Why does the US still use Fahrenheit when most of the world uses Celsius?
The US adopted Fahrenheit in the colonial era and, unlike most countries, never transitioned during the global metric shift of the 1970s–1980s. The Metric Conversion Act of 1975 made metrication voluntary rather than mandatory, so everyday usage remained Fahrenheit. Science, medicine, and the military in the US do use Celsius and SI units — only public weather forecasts and consumer appliances remain predominantly Fahrenheit.
What is the boiling point of water in both scales, and does altitude change it?
Water boils at 212 °F (100 °C) at sea level (1 atm of pressure). At higher altitudes, reduced atmospheric pressure lowers the boiling point: in Denver, CO (5,280 ft / 1,609 m), water boils at approximately 202 °F (94.4 °C). At the summit of Mount Everest (~29,032 ft / 8,849 m), it drops to about 160 °F (71 °C) — below the safe cooking temperature for poultry, which is why high-altitude cooking times must be adjusted.
Is there a quick mental math trick for rough Fahrenheit-to-Celsius conversions?
Yes — subtract 30 from the °F value, then divide by 2: °C ≈ (°F − 30) / 2. Example: 80 °F → (80 − 30) / 2 = 25 °C (exact: 26.7 °C). This shortcut stays within ±2 °C for typical weather temperatures (roughly 20–95 °F). For medical, cooking, or scientific use, always apply the exact formula °C = (°F − 32) × 5/9 to avoid meaningful errors.