Celsius to Fahrenheit Converter

To convert Celsius to Fahrenheit, multiply by 9/5 (1.8) and add 32: °F = °C × 9/5 + 32. For example, 20 °C × 1.8 = 36, plus 32 = 68 °F, a comfortable room temperature. This free Celsius to Fahrenheit converter runs the exact formula in both directions, adds Kelvin for science work, and shows every step so you can do it by hand.

A temperature conversion is a fixed scale swap, not a percentage: 30 °C is not "50% hotter" than 20 °C just because 30 is 50% more than 20. On the absolute Kelvin scale, 30 °C (303.15 K) is only about 3.4% warmer than 20 °C (293.15 K). For other everyday conversions, the kg to Pounds Converter handles weight, the Miles to km Converter handles distance and speed, and the Dew Point Calculator works from air temperature and relative humidity.

The Celsius to Fahrenheit formula

Converting from Celsius to Fahrenheit takes two steps: scale the number up, then shift it. The formula is:

The fraction 9/5 (equal to 1.8) accounts for the fact that one Celsius degree is 1.8 times larger than one Fahrenheit degree. The + 32 shifts the scale so that the freezing point of water lines up: 0 °C and 32 °F are the same temperature. To go the other way, you simply undo those two operations in reverse order:

And for scientific work, Kelvin shares the Celsius degree size but starts at absolute zero, so the conversion is just an offset:

A worked example, step by step

Suppose you want to convert 25 °C to Fahrenheit. Work through the formula in order:

1. Multiply by 9/5: 25 × 1.8 = 45.
2. Add 32: 45 + 32 = 77 °F.

So a warm 25 °C day is 77 °F. To check yourself, run it backwards: (77 − 32) ÷ 1.8 = 45 ÷ 1.8 = 25 °C. If the round trip returns your original number, the conversion is correct. For Kelvin, 25 + 273.15 = 298.15 K.

How to use this converter

The tool is fully bidirectional: you can type in any of the three fields and the others update instantly.

1. Pick a starting unit: click into the Celsius, Fahrenheit or Kelvin box, whichever you already know.
2. Type the value: enter a whole number or a decimal (for example 98.6 or −12.5). Negative numbers are fine for Celsius and Fahrenheit; anything below absolute zero (−273.15 °C, −459.67 °F, 0 K) is flagged.
3. Read the others: the remaining two fields recalculate as you type, and the large result panel shows the main conversion (°F when you type Celsius, °C when you type Fahrenheit or Kelvin) plus a step-by-step breakdown.
4. Use the quick buttons: shortcuts for freezing, room, body and boiling temperatures load common values in one click.

There is no "calculate" button to press and nothing to install: the conversion happens entirely in your browser the moment you type.

Who this converter is for

• Travelers reading a foreign weather forecast or hotel thermostat in the "wrong" scale.
• Home cooks following a recipe written for a Celsius oven on a Fahrenheit dial, or vice versa.
• Students doing physics, chemistry or earth-science homework that mixes Celsius, Fahrenheit and Kelvin.
• Parents checking a child's temperature when the thermometer and the guidance use different units.
• Makers and hobbyists setting a soldering iron, 3D printer or sous-vide bath that is labeled in one scale while the instructions use another.

Key terms explained

• Celsius (°C): the metric temperature scale, with 0° at the freezing point of water and 100° at its boiling point (at sea level). Used by most of the world.
• Fahrenheit (°F): the scale used mainly in the United States, with 32° at freezing and 212° at boiling. Its degrees are smaller and more numerous across the same range.
• Kelvin (K): the SI base unit of temperature, used in science. It has the same degree size as Celsius but begins at absolute zero, so it never goes negative. Note that Kelvin is written without a degree symbol.
• Absolute zero: the lowest possible temperature: 0 K, −273.15 °C, or −459.67 °F.
• Degree size: a 1 °C change equals a 1.8 °F change. That ratio of 9/5 is why the multiplication step exists in the formula.

Three more worked examples

Seeing the formula applied to familiar temperatures makes it stick:

• Body temperature (37 °C): 37 × 1.8 = 66.6, then + 32 = 98.6 °F. This is why the classic thermometer reading in the US is 98.6.
• A freezing night (−5 °C): −5 × 1.8 = −9, then + 32 = 23 °F. Notice the answer is still well below freezing, just expressed on a different scale.
• A baking oven (180 °C): 180 × 1.8 = 324, then + 32 = 356 °F. Recipes usually round this to a 350 °F dial setting. If the recipe also lists ingredient amounts in grams or milliliters, the Cooking Converter turns those into US cups and ounces.

Quick reference table

These are the temperatures most people convert again and again. The table inside the tool covers more points, but here is a printable summary:

Celsius to Fahrenheit chart (−20 °C to 45 °C)

This is the everyday range you meet in weather forecasts and thermostats, in 5-degree steps. Each pair is computed with °F = °C × 9/5 + 32, so 23 °C reads 73.4 °F and 45 °C reads 113 °F.

Fahrenheit to Celsius chart: common °F values

Reading the other direction with °C = (°F − 32) ÷ 1.8. A mild 68 °F is exactly 20 °C, and a cold −3 °F works out to −19.4 °C. Values are rounded to one decimal place.

Tips for fast mental conversions

• The quick estimate: double the Celsius number and add 30. For 20 °C that gives 70 (true value 68), close enough for weather.
• Anchor on −40: the two scales meet at −40°, a handy sanity check for any converter.
• Remember the pairs: 0/32, 10/50, 20/68, 30/86, 37/98.6, 100/212. Memorizing a few makes interpolation easy.
• Each 5 °C = 9 °F: a 5-degree jump in Celsius is a 9-degree jump in Fahrenheit, which mirrors the 9/5 ratio directly.

Common pitfalls to avoid

Most conversion errors come from doing the two steps in the wrong order or skipping one:

• Adding 32 before multiplying. Going C → F you multiply first, then add. Going F → C you subtract first, then divide. Reversing the order gives a wrong answer.
• Mixing up 9/5 and 5/9. Use 9/5 (1.8) to go from Celsius to Fahrenheit, and 5/9 (about 0.556, the same as dividing by 1.8) to go back.
• Adding a degree symbol to Kelvin. Kelvin is written as "300 K", never "300 °K".
• Forgetting negatives still convert normally. The formula works the same for −10 °C as for +10 °C; just keep the sign.

A little history of the scales

The Fahrenheit scale was proposed by Daniel Gabriel Fahrenheit in the early 1700s. According to NIST, he first set 0° at the freezing point of a salt-water solution and 96° at human body temperature; the fixed points were later adjusted so that pure water freezes at 32° and boils at 212° at sea level. The Celsius scale began with Anders Celsius, who in the 1740s divided the range between the freezing and boiling points of water into 100 degrees, but originally ran it "backwards," with boiling at 0 and freezing at 100; the points were swapped after his death, giving the 0 °C freezing and 100 °C boiling scale that fits the metric system. Kelvin comes from William Thomson (Lord Kelvin), whose 1848 paper "On an Absolute Thermometric Scale" set out a scale starting from absolute zero so that temperature could be treated as an absolute quantity in physics. All three measure the same thing, just from different starting points and with different degree sizes, and understanding that is the key to converting confidently.

Oven temperatures: Celsius, Fahrenheit and gas marks

Cooking is where most people meet a temperature conversion head-on, because a recipe written in one country rarely matches the dial on your stove. A US oven is marked in Fahrenheit, most of Europe uses Celsius, and older British recipes still call for "gas marks." The conversion itself is identical to any other (°F = °C × 9/5 + 32), but bakers care about a quirk: oven dials move in steps, so a mathematically exact 356 °F is usually set as 350 °F. The table below lines up the three systems for the temperatures that appear most often in baking and roasting, using the conventional gas mark equivalents.

One extra wrinkle: fan (convection) ovens cook faster than conventional ones, so many recipes tell you to lower the temperature when using the fan setting, often by about 20 °C. Note that a 20 °C difference is a 36 °F difference, because differences scale by 1.8 without the +32. Convert the temperature first, then apply the fan adjustment. For everything off the stove, from cup-to-gram swaps to butter sticks, the Cooking Converter is the companion tool to this page.

Weather, health and science: where each scale shows up

Although the math never changes, the context decides which scale you actually need. Knowing where each one dominates helps you sanity-check a converted number instead of trusting it blindly.

• Weather forecasts: the US reports air temperature in Fahrenheit; almost everywhere else uses Celsius. A "30-degree day" is a hot day in Celsius (86 °F) but a near-freezing day in Fahrenheit (about −1 °C). Always confirm which scale a forecast uses before you pack.
• Body temperature and fever: most countries use Celsius for body temperature (37 °C average, 38 °C fever threshold), while US thermometers usually read Fahrenheit (98.6 °F and 100.4 °F). CDC defines a fever as a measured temperature of 100.4 °F (38 °C) or higher. A converter removes the guesswork when a thermometer and the advice disagree on units.
• Science and engineering: Kelvin is the SI unit because gas laws and thermodynamic equations only work with an absolute scale that starts at zero. You will almost never see Kelvin on a weather app, but you will see it constantly in physics and chemistry problems.
• Industrial and culinary specs: data sheets, kilns, soldering irons and sous-vide baths may be labeled in either Celsius or Fahrenheit depending on where they were made, which is exactly the mismatch this converter is built to resolve.

Because each field has its own "home" scale, the most common real-world task is not pure arithmetic: it is translating a number from the scale it was written in into the one your instrument or audience expects. That is the job this page does in a single keystroke.

Body temperature in Celsius and Fahrenheit

Clinical guidance is often written in Celsius while US thermometers read Fahrenheit, so body temperature is a conversion parents and patients need regularly, sometimes to two decimals. Every °F below is computed with °C × 9/5 + 32. The labels follow CDC's fever definition (a measured 100.4 °F, 38 °C, or higher), CDC's hypothermia warning (below 95 °F, 35 °C, get medical attention immediately) and the typical normal range of about 97 to 99 °F (36.1 to 37.2 °C) described by the NIH's MedlinePlus.

These labels are general references, not medical advice; symptoms, age and where the temperature is taken (mouth, ear, armpit or rectum) matter as much as the number, so follow guidance from a clinician or the thermometer's instructions for any health decision.

Why the conversion is exact (and when rounding matters)

The Celsius-to-Fahrenheit relationship is a defined linear equation, not an approximation, so the conversion is mathematically exact: any temperature has one and only one correct Fahrenheit equivalent. The factor 1.8 and the offset of 32 are fixed by the definitions of the scales, which is why a well-built converter and a careful hand calculation will always agree to the last decimal. Rounding only enters when you display the result. For weather, rounding to a whole degree is fine; nobody needs 67.82 °F. For a fever check, one decimal place (98.6 °F) is the convention. For laboratory work, you may keep two or more decimals and only round at the very end of a calculation, because rounding early and then doing further math can let small errors accumulate. This converter follows that rule: it computes with full precision internally and rounds just once, at the moment it shows you the answer.

Related concepts and calculators

This page answers "what is this temperature in the other scale?" If you have a related question, a sister tool fits better:

• For weight, use the kg to Pounds Converter; for distance and speed, the Miles to km Converter.
• For lengths and heights, see the Feet to Meters Converter and the cm to Feet Converter.
• For many unit types in one place, use the Unit Converter.
• To find how humid the air feels from its temperature, use the Dew Point Calculator.
• To size a heater or air conditioner for a room, the BTU Calculator works from room size and climate.
• Scaling a recipe between metric and US units? The Cooking Converter handles cups, grams, ounces and more.

Sources

• National Institute of Standards and Technology (NIST): SI units, temperature (exact conversion equations; 0 °C = 273.15 K).
• NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement (conversion equations for units of temperature).
• NIST: Kelvin: History (Fahrenheit, Celsius and Kelvin scales).
• International Bureau of Weights and Measures (BIPM): SI base units, including the kelvin.
• CDC: Definitions of signs, symptoms and conditions (fever: a measured temperature of 100.4 °F [38 °C] or greater).
• CDC: Preventing hypothermia (below 95 °F, get medical attention immediately).
• NIH MedlinePlus: Body temperature norms (98.6 °F average; about 97 °F to 99 °F typical).
• U.S. Food and Drug Administration: Are you storing food safely? (refrigerator at or below 40 °F, 4 °C).