Celsius to Fahrenheit Converter

Celsius to Fahrenheit converter using the exact formula °F = °C × 9/5 + 32.

Convert Bidirectional Exact formula

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Celsius ↔ Fahrenheit

Exact formula · Bidirectional · Quick picks for weather, body temp, cooking

Instructions — Celsius to Fahrenheit Converter

Enter Celsius or Fahrenheit

Type into either box. The other updates instantly. The default is 25 °C, a comfortable room temperature in metric countries (= 77 °F). Both scales agree at exactly one point: −40 °C = −40 °F.

Use the quick picks

The buttons cover the milestones used most: 0 °C (water freezes), 20 °C (typical indoor temperature), 25 °C (warm room), 37 °C (normal body temperature), 100 °C (water boils at sea level), 200 °C (medium-hot oven). −40 °C is the fixed point where both scales agree.

Adjust precision

Two decimals is the default. Weather and cooking need one at most. Lab work might want four. Click the Precision dropdown to change. The factor 9/5 is exact (= 1.8), so extra digits never lose accuracy.

Mental shortcut (C → F): double it, add 30. 25 °C → 25 × 2 + 30 = 80 °F. Exact answer 77 °F. Good enough to pick a jacket.

Mental shortcut (F → C): subtract 30, divide by 2. 80 °F → (80 − 30)/2 = 25 °C. Exact answer 26.7 °C. Within 2 °C across normal weather.

Formulas

The two temperature scales are linked by a simple linear equation. Celsius is defined within the SI: water freezes at 0 °C and boils at 100 °C at one atmosphere. Fahrenheit predates SI by 18 years and assigns the same two points to 32 °F and 212 °F — 180 degrees instead of 100. The ratio 180/100 = 9/5 is the slope between the scales, and 32 is the offset.

Celsius to Fahrenheit

$$ T_{°F} = T_{°C} \times \frac{9}{5} + 32 $$

Multiply by 9/5 (= 1.8) first, then add 32. A 1 °C change equals 1.8 °F of change. A 10 °C drop is an 18 °F drop, not a 10 °F drop.

Fahrenheit to Celsius

$$ T_{°C} = (T_{°F} - 32) \times \frac{5}{9} $$

Subtract 32 first, then multiply by 5/9 (≈ 0.5556). Order matters — multiplying first gives the wrong answer. 5/9 = 0.555… recurring.

Celsius to Kelvin

$$ T_K = T_{°C} + 273.15 $$

Kelvin is the SI base unit for temperature. Same step size as Celsius, but zero is absolute zero. 0 K = −273.15 °C = −459.67 °F.

Where the scales meet

$$ -40\,°C = -40\,°F $$

Set T = 9/5 × T + 32 and solve: T = −40. The one and only point where both scales show the same number. Northern Manitoba, the Yukon, and Siberia hit this most winters.

Quick mental approximation

$$ T_{°F} \approx T_{°C} \times 2 + 30 $$

Works for weather (−10 to 35 °C) with error under 3 °F. Quicker than the exact formula when you just need to know if a forecast is shorts weather or a sweater day.

More accurate mental version

$$ T_{°F} = T_{°C} \times 2 - 10\%(T_{°C} \times 2) + 32 $$

Double it, subtract 10% of the doubled value, add 32. 25 °C → 50 − 5 + 32 = 77 °F. Algebraically identical to × 1.8 + 32, so it gives an exact answer with grade-school math.

Reference

Common Temperatures — Celsius to Fahrenheit to Kelvin

Context	°C	°F	K
Absolute zero	−273.15	−459.67	0
Coldest on Earth (Vostok, 1983)	−89.2	−128.6	183.95
Scales meet	−40	−40	233.15
Deep freezer	−18	0	255.15
Water freezes	0	32	273.15
Refrigerator	4	39.2	277.15
Cool day	10	50	283.15
Indoor heating target	20	68	293.15
Comfortable room	22	71.6	295.15
Warm room / mild day	25	77	298.15
Hot summer day	30	86	303.15
Body temp (classic)	37.0	98.6	310.15
Fever threshold	38.0	100.4	311.15
Heatwave (extreme)	40	104	313.15
Pasteurisation (HTST)	72	161.6	345.15
Water boils (1 atm)	100	212	373.15
Oven (low bake)	160	320	433.15
Oven (cakes, cookies)	180	356	453.15
Oven (roast)	200	392	473.15
Oven (pizza)	250	482	523.15

Weather quick chart

The most-used range, every 5 °C. Useful for reading a metric forecast in an imperial country (or vice versa).

Cold range

°C	°F	Feel
−20	−4	Bitter cold
−10	14	Very cold
−5	23	Frost
0	32	Freezing
5	41	Chilly
10	50	Light jacket

Warm range

°C	°F	Feel
15	59	Mild
20	68	Comfortable
25	77	Warm
30	86	Hot
35	95	Very hot
40	104	Heatwave

USDA safe internal cooking temperatures

Product	°C	°F
Beef, pork, lamb (steaks, chops)	63	145
Ground meat (beef, pork)	71	160
Poultry (whole and pieces)	74	165
Leftovers and casseroles	74	165

Source: USDA FSIS Safe Minimum Internal Temperature Chart. Use a meat thermometer; the temperature is measured at the thickest part, not the surface.

Article — Celsius to Fahrenheit Converter

Celsius to Fahrenheit: Formula, Everyday Use, and the Metric Perspective

In this article

The exact formula
Why Celsius is the default for most of the world
Reading a US weather forecast from a metric country
Fever, body temperature, and 38 °C
Oven temperatures: 180 °C vs 350 °F
Minus forty: the only point both scales agree
Celsius, kelvin, and the 2019 SI redefinition
Common conversion mistakes

To convert Celsius to Fahrenheit, multiply by 9/5 (which is 1.8) and add 32. The formula is °F = °C × 9/5 + 32. Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F). Comfortable indoor 22 °C equals 71.6 °F. Body temperature 37 °C equals 98.6 °F.

Around 190 countries use Celsius as standard. The exceptions are the US, Liberia, Palau, the Marshall Islands, and the Federated States of Micronesia; the Bahamas, and the Cayman Islands also use Fahrenheit. If you live in a metric country and need to read a US recipe or a Florida weather forecast, the math is short — but the order of operations and the offset trip people up.

The exact formula

Celsius to Fahrenheit: °F = °C × 9/5 + 32. The reverse: °C = (°F − 32) × 5/9. Both versions are exact, not rounded. The factor 9/5 equals 1.8 exactly; 5/9 equals 0.5555… recurring. The 32 is the offset between the zeros of the two scales — water freezes at 0 °C and at 32 °F. The 9/5 is the slope: a 5 °C change equals a 9 °F change. Equivalently, 1 °C corresponds to 1.8 °F of change.

Did you know

Order of operations matters. Multiplying by 9/5 before adding 32 is correct. Adding first gives the wrong answer. For 25 °C: the correct path is 25 × 1.8 + 32 = 77 °F. The wrong path is (25 + 32) × 1.8 = 102.6 °F, off by 26 degrees.

Why Celsius is the global default

Anders Celsius, a Swedish astronomer at Uppsala, proposed the 100-point scale in 1742. His original version was inverted: 0 was boiling, 100 freezing. Carl Linnaeus flipped it in 1745. The name was changed from "centigrade" to "Celsius" in 1948 by the 9th General Conference on Weights and Measures, to avoid confusion with the centigrade as a unit of angle. The scale spread with the metric system through the 1800s and 1900s. Britain switched in the 1960s. The US never finished — the Metric Conversion Act of 1975 made the switch voluntary.

Reading a US weather forecast from a metric country

Most non-US weather services report in Celsius; American TV, radio, and apps default to Fahrenheit. A few anchor points are worth memorising: 20 °C is room temperature (68 °F), 25 °C a warm summer day (77 °F), 30 °C hot (86 °F), 35 °C heatwave territory (95 °F), 40 °C dangerous heat (104 °F). For mental math, doubling and adding 30 gets you within 3 °F across normal weather.

Celsius

~190 countries

Europe, Asia, South America, Africa, Australia, Canada

Fahrenheit

~7 countries

US, Liberia, Palau, Marshall Islands, Micronesia, Bahamas, Cayman Islands

Tip

The mental shortcut "double and add 30" is exact at 10 °C: 10 × 2 + 30 = 50 °F, and 50 °F is the exact answer. The error grows by about 1 °F per 5 °C you move away from that anchor. So 25 °C → 80 °F (real: 77 °F, error 3 °F), 35 °C → 100 °F (real: 95 °F, error 5 °F).

Fever, body temperature, and 38 °C

Normal body temperature is widely taught as 37.0 °C (98.6 °F), the number from Carl Wunderlich's 1868 averages of 25,000 patients. A 2020 Stanford Medicine reanalysis of 677,423 US measurements found the modern average has fallen to 36.6 °C (97.9 °F), with a normal range of 36.3 to 36.8 °C. The clinical fever threshold has not shifted. The World Health Organization defines fever as a measured body temperature at or above 38.0 °C (100.4 °F). A temperature of 40 °C (104 °F) or higher in an adult is a medical emergency.

Do not confuse 100 with 100.4

A reading of 100 °F is below the fever threshold (it equals 37.78 °C). The cutoff is 100.4 °F, equal to 38.0 °C — exactly the WHO definition. The 0.4 °F gap matters in clinical guidance and in school sick-leave policies. Round-tripping through metric and back can lose this distinction, so trust the source unit.

Oven temperatures: 180 °C vs 350 °F

European recipes give oven temperatures in Celsius; American recipes use Fahrenheit. The most common European baking setting, 180 °C, equals 356 °F, which US recipes round to 350 °F. Standard conversions: 150 °C = 302 °F (US 300), 180 °C = 356 °F (US 350), 200 °C = 392 °F (US 400), 220 °C = 428 °F (US 425), 250 °C = 482 °F (US 475). British recipes sometimes use gas marks: gas mark 4 corresponds to 180 °C / 350 °F, gas mark 7 to 220 °C / 425 °F.

Common oven conversions

150 °C 302 °F (≈300)

180 °C 356 °F (≈350)

200 °C 392 °F (≈400)

220 °C 428 °F (≈425)

250 °C 482 °F (≈475)

Minus forty: the only point both scales agree

The two scales meet at exactly one temperature: −40 °C = −40 °F. Set them equal: T = 9/5 × T + 32, and T = −40. There is only one solution because both formulas are linear with different slopes. This is not a designed coincidence — it falls out of the algebra. The temperature is real and reachable. Northern Manitoba, the Yukon, parts of Siberia, and interior Alaska hit −40 most winters. The lowest temperature recorded on Earth was −89.2 °C (−128.6 °F) at Vostok Station, Antarctica, on 21 July 1983.

Celsius, kelvin, and the SI redefinition

Celsius is the metric scale for everyday use, but the SI base unit for temperature is the kelvin. Kelvin uses the same step size as Celsius — a one-degree change is identical — but starts at absolute zero. 0 K = −273.15 °C = −459.67 °F, and K = °C + 273.15. The kelvin was redefined in 2019 through the Boltzmann constant, k = 1.380 649 × 10⁻²³ J/K, giving it an exact value independent of any physical sample. Celsius is now defined through kelvin: t/°C = T/K − 273.15.

Did you know

Anders Celsius died of tuberculosis in 1744, just two years after proposing his scale, and never saw the orientation used today — Linnaeus inverted it the year after Celsius died. The Uppsala observatory where the scale was first used has been recording temperatures continuously since 1722, the longest unbroken record in the world.

Common conversion mistakes

Order of operations is the biggest one. Multiply first, add second. A 10 °C change is not a 10 °F change — it is 18 °F (10 × 1.8). The 32 offset cancels for differences, but the 1.8 slope does not. Reading 100 °F as fever is another common slip: the WHO cutoff is 100.4 °F (38.0 °C), and 100 °F equals 37.78 °C.

0 °C = 32 °F, water freezes
20 °C = 68 °F, comfortable room temperature
37 °C = 98.6 °F, classic normal body temperature
38 °C = 100.4 °F, WHO fever threshold
100 °C = 212 °F, water boils at 1 atm
180 °C = 356 °F, standard European baking
−40 the only point where °C and °F agree
−273.15 °C = 0 K, absolute zero
9/5 = 1.8, the slope between °C and °F

Sources

FAQ

Q1 How do you convert Celsius to Fahrenheit?

Multiply by 9/5 (which is 1.8) and add 32. Formula: °F = °C × 9/5 + 32. Example: 25 °C × 1.8 + 32 = 77 °F. The order matters — adding 32 first gives the wrong answer.

Q2 What is 0 °C in Fahrenheit?

0 °C = 32 °F. This is the freezing point of water at one atmosphere and one of the two anchor points used to define both scales.

Q3 What is 100 °C in Fahrenheit?

100 °C = 212 °F. Water boils at this temperature at sea-level atmospheric pressure (1 atm). At higher altitudes water boils a few degrees lower because the pressure drops.

Q4 What is 37 °C in Fahrenheit?

37 °C = 98.6 °F, the classic textbook body temperature from Carl Wunderlich (1868). A 2020 Stanford reanalysis of 677,423 modern measurements pushed the average down to 36.6 °C (97.9 °F). The clinical fever threshold remains 38.0 °C (100.4 °F).

Q5 What is 38 °C in Fahrenheit?

38 °C = 100.4 °F. The World Health Organization defines fever as a measured body temperature at or above 38.0 °C. Anything between 37.5 and 38.0 °C (99.5 to 100.4 °F) is called a low-grade temperature.

Q6 At what temperature do Celsius and Fahrenheit match?

At −40 degrees. The scales cross at exactly one point: −40 °C = −40 °F. Solve the equation T = 9/5 × T + 32 and you get T = −40. Northern Manitoba, Siberia, and interior Alaska hit this most winters.

Q7 How do you convert oven temperatures from Celsius to Fahrenheit?

The common European baking temperatures convert as: 150 °C = 302 °F (often rounded to 300), 180 °C = 356 °F (rounded to 350), 200 °C = 392 °F (rounded to 400), 220 °C = 428 °F (rounded to 425), 250 °C = 482 °F (rounded to 475). US recipes round to the nearest 25 °F.

Q8 Why does the world use Celsius instead of Fahrenheit?

Celsius lines up with the metric system — water freezes at 0 and boils at 100, which makes science and engineering simpler. Most of the world adopted metric in the 1800s and 1900s. The United States kept Fahrenheit for daily use; the Metric Conversion Act of 1975 made the switch voluntary and it never finished.

Q9 What is the difference between Celsius and centigrade?

They are the same scale. The name was officially changed from centigrade to Celsius at the 9th General Conference on Weights and Measures (CGPM) in 1948 to avoid confusion with the centigrade as a unit of angle used in surveying (1/100 of a gon).

Q10 What is the relationship between Celsius and Kelvin?

Same step size, different zero. K = °C + 273.15. 0 K is absolute zero, the lowest possible temperature. Kelvin is the SI base unit and the only true thermodynamic temperature scale. Since 2019, Celsius has been defined through kelvin via the Boltzmann constant.