What is the Celsius to Fahrenheit formula?

Fahrenheit equals Celsius multiplied by 9/5, then plus 32. So 25°C becomes 25 × 1.8 + 32 = 77°F. The reverse subtracts first: Celsius equals Fahrenheit minus 32, multiplied by 5/9. Order matters — multiply before adding, subtract before multiplying.

What is normal body temperature in both scales?

37°C is 98.6°F, the traditional normal. The fever threshold most medical guidance uses is 38°C, which is 100.4°F. Modern research suggests average body temperature is slightly below 37°C, so treat 98.6°F as a convention rather than a precise constant.

Why does −40 convert to itself?

Because the two scales cross at exactly that point. They have different zero points and different degree sizes, so plotted as lines they intersect once, at −40. It makes a useful sanity check: any converter that does not return −40°F for −40°C is wrong.

What is a quick mental shortcut?

Double the Celsius figure and add 30. So 20°C gives about 70°F against an exact 68°F. It stays within a few degrees across everyday weather from 0 to 35°C, then drifts badly: at 100°C it gives 230°F instead of 212°F.

What oven temperatures do recipes use?

160°C is 320°F, 180°C is 356°F but written as 350°F, 200°C is 392°F written as 400°F, and 220°C is 428°F written as 425°F. US recipes round to the nearest 25°F, so single-degree precision is meaningless when baking.

Which countries still use Fahrenheit?

The United States, plus a handful of territories including Puerto Rico, the Cayman Islands and Liberia. Everywhere else uses Celsius for weather. The UK is a partial exception where older domestic thermometers and some newspapers still quote Fahrenheit in hot weather.

Kelvin uses the same degree size as Celsius but starts at absolute zero, so you convert by adding 273.15. That makes 0°C equal to 273.15 K and 100°C equal to 373.15 K. Kelvin needs no degree symbol and never goes negative.

Is my input stored anywhere?

No. The conversion is a single formula running in your browser as you type, so nothing is uploaded, logged, or tracked. The page keeps working with no connection once it has loaded, which is a reasonable proof that nothing is being sent.

Celsius to Fahrenheit Converter

Convert Celsius to Fahrenheit online free — instant two-way temperature conversion with formula shown. Nothing leaves your device — fast and private.

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Celsius (°C)

Fahrenheit (°F)

Quick values

To convert Celsius to Fahrenheit, multiply by 9/5 and add 32. So 25°C is 77°F. Type a value in either box above and both sides update instantly using the exact formula, with quick buttons for the temperatures people actually look up. Everything runs in your browser.

How the conversion works

The formula is °F = °C × 9/5 + 32, and the reverse is °C = (°F − 32) × 5/9. Both directions work here, so you can go either way without switching tools. The quick-select buttons cover body temperature at 37°C, room temperatures, weather extremes, the boiling point, and the curious −40° crossover where the two scales read the same number.

Celsius to Fahrenheit reference chart

The values people look up most, with what they correspond to.
°C	°F	What it means
−40	−40	The scales intersect
0	32	Water freezes
10	50	Cool day
20	68	Room temperature
25	77	Warm day
30	86	Hot day
37	98.6	Body temperature
38	100.4	Fever threshold
40	104	Dangerous heat
100	212	Water boils
180	356	Baking, written as 350°F

Why the formula has two parts

The scales differ in two independent ways, and each accounts for one part of the formula. First, thezero points differ: water freezes at 0°C but 32°F, which is where the +32 comes from. Second, the degrees are different sizes: there are 100 Celsius degrees between freezing and boiling but 180 Fahrenheit degrees across the same range, so one Celsius degree equals 1.8 Fahrenheit degrees, which is the × 9/5. Understanding that also explains the classic mistake: adding 32 before multiplying inflates the +32 into +57.6, so every answer comes out 25.6 degrees too high regardless of the temperature.

Reading a forecast in the other scale

If you are travelling or reading foreign weather coverage, a handful of anchor points is more useful than a formula. These are the ones worth memorising:

32°F is freezing. Below it, roads ice and precipitation may fall as snow.
50°F is a cool day needing a jacket, around 10°C.
68°F is comfortable room temperature, 20°C, and the usual thermostat setting.
86°F is properly hot, 30°C, the point at which shade and water matter.
100°F is just under 38°C, roughly the fever threshold and genuinely dangerous heat outdoors.

Notice that Fahrenheit's practical weather range runs from about 0 to 100, which is part of why it persists for everyday use in the US: the scale happens to map neatly onto human comfort, where Celsius spends most of its weather range between −10 and 40.

The double-it-and-add-30 shortcut

For conversation, doubling the Celsius figure and adding 30 is genuinely useful. It works because doubling approximates the × 1.8, and the +30 stands in for the +32, with the two errors partly cancelling. Across ordinary weather it lands within about three degrees: 15°C gives 60°F against an exact 59°F, and 30°C gives 90°F against 86°F. It falls apart at the extremes, giving 230°F for boiling water instead of 212°F. Use it to picture a forecast; use the exact formula for anything medical, scientific, or written down.

Cooking is the one place precision does not matter

Recipe temperatures are the most common reason people convert, and they are also the most forgiving. US recipes round to the nearest 25°F, so a European 180°C oven is written as 350°F even though it converts to 356°F. Ovens themselves typically drift by 10 to 15 degrees Fahrenheit anyway, and most have dials marked in 25-degree steps. Convert, round to the nearest marking, and stop worrying — the difference is smaller than your oven's own error.

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Frequently Asked Questions

What is the Celsius to Fahrenheit formula?
Fahrenheit equals Celsius multiplied by 9/5, then plus 32. So 25°C becomes 25 × 1.8 + 32 = 77°F. The reverse subtracts first: Celsius equals Fahrenheit minus 32, multiplied by 5/9. Order matters — multiply before adding, subtract before multiplying.
What is normal body temperature in both scales?
37°C is 98.6°F, the traditional normal. The fever threshold most medical guidance uses is 38°C, which is 100.4°F. Modern research suggests average body temperature is slightly below 37°C, so treat 98.6°F as a convention rather than a precise constant.
Why does −40 convert to itself?
Because the two scales cross at exactly that point. They have different zero points and different degree sizes, so plotted as lines they intersect once, at −40. It makes a useful sanity check: any converter that does not return −40°F for −40°C is wrong.
What is a quick mental shortcut?
Double the Celsius figure and add 30. So 20°C gives about 70°F against an exact 68°F. It stays within a few degrees across everyday weather from 0 to 35°C, then drifts badly: at 100°C it gives 230°F instead of 212°F.
What oven temperatures do recipes use?
160°C is 320°F, 180°C is 356°F but written as 350°F, 200°C is 392°F written as 400°F, and 220°C is 428°F written as 425°F. US recipes round to the nearest 25°F, so single-degree precision is meaningless when baking.
Which countries still use Fahrenheit?
The United States, plus a handful of territories including Puerto Rico, the Cayman Islands and Liberia. Everywhere else uses Celsius for weather. The UK is a partial exception where older domestic thermometers and some newspapers still quote Fahrenheit in hot weather.
What about Kelvin?
Kelvin uses the same degree size as Celsius but starts at absolute zero, so you convert by adding 273.15. That makes 0°C equal to 273.15 K and 100°C equal to 373.15 K. Kelvin needs no degree symbol and never goes negative.
Is my input stored anywhere?
No. The conversion is a single formula running in your browser as you type, so nothing is uploaded, logged, or tracked. The page keeps working with no connection once it has loaded, which is a reasonable proof that nothing is being sent.