Math

Convert Fahrenheit to Celsius (and Back)

Q: What is the exact formula to convert Fahrenheit to Celsius?

**°C = (°F − 32) × 5/9**. No approximation — the relationship is a fixed linear equation. Example: 77 °F → (77 − 32) × 5/9 = 45 × 0.5556 = **25 °C** exactly.

Q: How do I convert Celsius to Fahrenheit?

Use **°F = (°C × 9/5) + 32**. Example: 100 °C (boiling point of water) → (100 × 1.8) + 32 = 180 + 32 = **212 °F**. Example: 37 °C (body temperature) → (37 × 1.8) + 32 = 66.6 + 32 = **98.6 °F**.

Q: At what temperature are Fahrenheit and Celsius the same number?

The two scales are equal at exactly **−40 degrees** — that is, −40 °F = −40 °C. Verify: (−40 − 32) × 5/9 = −72 × 0.5556 = −40 °C. This is the only point where both scales share the same numerical value.

Q: What is normal human body temperature in both scales?

The long-established standard is **98.6 °F = 37.0 °C**. A 2020 Stanford/eLife study found the modern average is closer to 97.9 °F (36.6 °C). The CDC uses **100.4 °F (38 °C)** as the clinical fever threshold.

Q: What temperatures does the USDA consider safe for cooking meat?

USDA 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; **165 °F (73.9 °C)** for all poultry, stuffing, and leftovers.

Q: 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**. At altitude, reduced pressure lowers the boiling point: in Denver, CO (~5,280 ft), water boils at about **202 °F (94.4 °C)**. At Everest's summit (~29,032 ft), it drops to roughly **160 °F (71 °C)** — below the USDA safe temperature for poultry, which is why high-altitude cooking times must be adjusted.

Q: Is there a quick mental math trick for Fahrenheit-to-Celsius?

Yes: **°C ≈ (°F − 30) / 2**. Example: 80 °F → (80 − 30) / 2 = 25 °C (exact: 26.7 °C). This stays within ±2 °C for typical weather temperatures (roughly 20–95 °F). For medical, cooking, or scientific use, always use the exact formula.

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Reviewed by: Martín Rodríguez (política editorial ) · Last reviewed: 4 jun 2026

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This converter gives you the exact temperature equivalent between Fahrenheit (°F) and Celsius (°C) — the two most widely used temperature scales in everyday life. The formula for Fahrenheit to Celsius is °C = (°F − 32) × 5/9; the reverse (Celsius to Fahrenheit) is °F = (°C × 9/5) + 32. Use it to read a weather forecast from another country, follow an international recipe, interpret a medical thermometer, or calibrate an oven. The Fahrenheit scale is standard in the United States; Celsius is used everywhere else and in all scientific disciplines.

Last reviewed: June 3, 2026 Verified by Martín Rodríguez Source: NIST – SI Units and Temperature Scales (Special Publication 330), USDA FSIS – Safe Minimum Internal Temperature Chart, NOAA National Weather Service – Temperature Conversion, CDC – Fever: First Aid (MedlinePlus / NIH), Wikipedia – Fahrenheit scale history and definition 100% private

To convert Fahrenheit to Celsius, subtract 32 then multiply by 5/9: **°C = (°F − 32) × 5/9**. Key benchmarks: 32 °F = 0 °C (water freezes), 98.6 °F = 37 °C (body temp), 212 °F = 100 °C (water boils). The two scales are equal at −40°.

When to use this calculator

Weather forecasts — a European city reporting 28 °C equals 82.4 °F, so you know to pack light summer clothes.
Cooking from international recipes — a UK recipe calling for 180 °C oven equals 356 °F on a US oven dial.
Medical readings — a fever of 38.5 °C equals 101.3 °F, signaling a moderate fever.
HVAC and smart thermostats — comfort range of 68–72 °F equals 20–22.2 °C.
Food safety — USDA requires poultry to reach 165 °F (73.9 °C) internally before it is safe to eat.
Scientific lab work — converting ambient temperature specs written in Celsius to Fahrenheit for US-manufactured equipment.
Travel and outdoor planning — a NOAA forecast of 14 °F wind-chill equals −10 °C, warning of frostbite risk within 30 minutes.

Worked Example

Input: 98.6 °F (normal body temperature)
Formula: (98.6 − 32) × 5/9 = 66.6 × 0.5556
Result: 37.0 °C

Result: 37.0 °C

How it works

2 min read

The Formulas

Both conversion formulas are exact — no rounding is introduced by the math:

Fahrenheit → Celsius:   °C = (°F − 32) × 5/9
Celsius → Fahrenheit:   °F = (°C × 9/5) + 32

Why subtract 32 first? Fahrenheit sets water's freezing point at 32 °F rather than 0 °F, so you 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: Subtract 30 from °F, then divide by 2 to get an approximate Celsius (e.g., 80 °F → (80 − 30) / 2 = 25 °C; exact: 26.7 °C). Accurate within ±2 °C for typical weather temperatures.

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Fahrenheit to Celsius Reference Chart

Fahrenheit (°F)	Celsius (°C)	What It Means
−40	−40	Only point where both scales are equal
0	−17.8	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
86	30	Hot summer day
98.6	37	Normal human body temperature
100	37.8	Slightly above normal body temp
104	40	High fever — seek medical care
140	60	Minimum safe temp for fish (USDA)
165	73.9	Safe internal temp for poultry (USDA)
212	100	Water boils at sea level
350	176.7	Typical baking temperature
400	204.4	High-heat roasting
451	232.8	Paper ignition point

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Worked 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 = 71.6 °F — 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 = 392 °F — 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 = 39.4 °C — 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. °F × 5/9 without removing the offset gives a completely wrong result (100 °F incorrectly becomes 55.6 °C instead of 37.8 °C).
2. Using 9/5 instead of 5/9 when converting F→C — always use 5/9 to go to Celsius and 9/5 to go to Fahrenheit.
3. Rounding too early in a chain calculation — use the full fraction 5/9 or at least 4 decimal places (0.5556) for medical or scientific work.
4. Confusing Celsius with Kelvin — Celsius and Kelvin share the same degree size, but 0 °C = 273.15 K. If a formula requires Kelvin, add 273.15 to your Celsius result.
5. Using the mental shortcut for extreme temperatures — the "subtract 30, divide by 2" trick works between −10 °C and 40 °C; outside that range, use the exact formula.

Frequently asked questions

What is the exact formula to convert Fahrenheit to Celsius?

°C = (°F − 32) × 5/9. No approximation — the relationship is a fixed linear equation. Example: 77 °F → (77 − 32) × 5/9 = 45 × 0.5556 = 25 °C exactly.

How do I convert Celsius to Fahrenheit?

Use °F = (°C × 9/5) + 32. Example: 100 °C (boiling point of water) → (100 × 1.8) + 32 = 180 + 32 = 212 °F. Example: 37 °C (body temperature) → (37 × 1.8) + 32 = 66.6 + 32 = 98.6 °F.

At what temperature are Fahrenheit and Celsius the same number?

The two scales are equal at exactly −40 degrees — that is, −40 °F = −40 °C. Verify: (−40 − 32) × 5/9 = −72 × 0.5556 = −40 °C. This is the only point where both scales share the same numerical value.

What is normal human body temperature in both scales?

The long-established standard is 98.6 °F = 37.0 °C. A 2020 Stanford/eLife study found the modern average is closer to 97.9 °F (36.6 °C). The CDC uses 100.4 °F (38 °C) as the clinical fever threshold.

What oven temperatures in Celsius correspond to common Fahrenheit settings?

Common oven conversions: 300 °F = 149 °C (low/slow cook), 325 °F = 163 °C (slow roast), 350 °F = 177 °C (standard baking), 375 °F = 191 °C, 400 °F = 204 °C (high-heat roasting), 425 °F = 218 °C, 450 °F = 232 °C (pizza/very hot). In fan/convection ovens, reduce by 25 °F (15 °C).

What temperatures does the USDA consider safe for cooking meat?

USDA 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; 165 °F (73.9 °C) for all poultry, stuffing, and leftovers.

Why does the US still use Fahrenheit when most of the world uses Celsius?

The US adopted Fahrenheit in the colonial era and never transitioned during the global metric shift of the 1970s–1980s. The Metric Conversion Act of 1975 made metrication voluntary, so everyday usage remained Fahrenheit. Science, medicine, and the military in the US do use Celsius — 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. At altitude, reduced pressure lowers the boiling point: in Denver, CO (~5,280 ft), water boils at about 202 °F (94.4 °C). At Everest's summit (~29,032 ft), it drops to roughly 160 °F (71 °C) — below the USDA safe temperature for poultry, which is why high-altitude cooking times must be adjusted.

Is there a quick mental math trick for Fahrenheit-to-Celsius?

Yes: °C ≈ (°F − 30) / 2. Example: 80 °F → (80 − 30) / 2 = 25 °C (exact: 26.7 °C). This stays within ±2 °C for typical weather temperatures (roughly 20–95 °F). For medical, cooking, or scientific use, always use the exact formula.