Temperature Converter

What is a temperature converter?

A temperature converter turns a reading on one scale into the same reading on another. The three you'll meet in daily life are Celsius (the scientific and global standard), Fahrenheit (the United States, the Bahamas, and a few small territories), and Kelvin (laboratory work, astronomy, anything where absolute zero matters). They measure the same physical quantity — the average kinetic energy of molecules — but they each start counting from a different place and use different-sized steps.

The Temperature Converter handles all three at once. Type a number into any field; the other two update as you type. There's no convert button, no sign-up, no dropdown menu hiding the imperial option three clicks deep. If you've ever had to Google "180 C to F" mid-recipe, this page is the version of that search that doesn't make you click through three ad-stuffed listicles first.

How to use the Temperature Converter

The interface has three input fields: Celsius, Fahrenheit, and Kelvin. Each one is a live two-way input.

1. Type a value into whichever scale you have. Maybe your oven manual says 200 °C, maybe a recipe says 350 °F, maybe your physics homework gives you 298 K.
2. Read the other two values, which update as you type.
3. Tap the copy icon next to any field to copy that value to your clipboard.

The inputs accept decimals and negative numbers. If you type something the converter can't make sense of (a letter, a Kelvin value below zero), the field shows a small inline warning rather than producing a silent wrong answer.

Your numbers stay in your browser. Nothing is sent to a server, logged, or cached anywhere outside your tab.

The formulas behind the conversions

Three scales means six conversion pairs, but they all reduce to two rules: a shift and a stretch.

The 9/5 ratio comes from how the two scales were originally calibrated. Celsius set water's freezing point at 0 and boiling point at 100, splitting the gap into 100 equal degrees. Fahrenheit set the same two points at 32 and 212, splitting the gap into 180 equal degrees. 180 divided by 100 is 1.8, also written as 9/5. The +32 shift accounts for the two scales' different zero points.

Kelvin uses the same step size as Celsius but starts at absolute zero (−273.15 °C) instead of water's freezing point. So a 1-degree change is identical in Celsius and Kelvin — only the zero moves.

Worked example: 100 °F into the other two scales.

• Fahrenheit to Celsius: (100 − 32) × 5/9 = 68 × 5/9 = 340/9 = 37.78 °C
• Celsius to Kelvin: 37.78 + 273.15 = 310.93 K

That number isn't random — 100 °F is roughly the upper edge of normal human body temperature, so 37.78 °C and 310.93 K describe a person running a mild fever. The converter agrees, to two decimal places, which is enough precision for everything outside a research lab.

A reference table you'll actually use

Some temperatures come up over and over. Bookmark this page or skim the table below the next time a recipe is in the wrong units.

The oven rows are the ones most people open this page for. American recipes give Fahrenheit, European recipes give Celsius, and a moderate oven is the same warm box either way — only the numbers on the dial change.

The three scales: history and where each one shows up

Celsius was invented in 1742 by Anders Celsius, a Swedish astronomer. The original version had 0 at the boiling point of water and 100 at freezing — upside down compared to today. Carl Linnaeus flipped it the right way around within a few years. The scale is now official across every country except the US, the Bahamas, Belize, the Cayman Islands, and Palau, and it's the default in science, weather forecasts, and cooking nearly everywhere.

Fahrenheit came earlier, in 1724, from a German physicist named Daniel Gabriel Fahrenheit. He set 0 at the freezing point of brine (the coldest he could reproducibly make in his Amsterdam workshop) and 96 at human body temperature. Later refinements moved body temperature to about 98.6 °F and locked the scale to water's freezing and boiling points at 32 and 212. The scale survives in the US largely because re-labeling thermostats, ovens, and weather reports is expensive and unpopular.

Kelvin is the SI unit of temperature, defined in 1848 by William Thomson (Lord Kelvin) after he worked out that there's a hard lower limit to how cold anything can get. That limit is absolute zero — the point at which all classical molecular motion stops. The scale uses the same step size as Celsius but shifts the zero point to that absolute floor. You almost never see Kelvin outside a laboratory or an astronomy textbook, but it's the right scale for the work it does — there are no negative values, and ratios are physically meaningful (300 K is twice as hot as 150 K in a way that 27 °C is not twice as hot as 13.5 °C).

Absolute zero and why temperature has a floor

Temperature is, at the molecular level, a measure of how energetically particles are jiggling around. Hot tea has water molecules moving fast; ice has them moving slowly; absolute zero is the theoretical limit where they'd stop entirely. Quantum mechanics means they don't really stop (zero-point energy is a thing), but classical motion would.

That floor sits at exactly −273.15 °C, exactly −459.67 °F, and exactly 0 K. No experiment has ever reached it — getting close becomes harder the colder you go, in a way that resembles trying to reach the speed of light. The current record, set at MIT in 2015, brought a sodium gas to within half a billionth of a degree above absolute zero. Outer space, by contrast, is a balmy 2.7 K (the leftover heat of the Big Bang, called the cosmic microwave background).

The Temperature Converter blocks negative Kelvin values for this reason. If you type something like −5 K, the field flags an error instead of giving you a meaningless conversion. Negative Celsius and Fahrenheit are fine and common — you just can't go below the absolute floor in Kelvin.

Common situations and the right scale for each

Different fields settle on different scales not because one is better but because each is well-tuned to a particular range of numbers.

• Cooking — Celsius in most of the world, Fahrenheit in the US. A moderate oven is 175 °C or 350 °F. The Temperature Converter is mostly used here for recipe conversions when an American food blog and a European cookbook collide.
• Weather — Celsius globally, Fahrenheit in the US. The two scales coincidentally cross at −40, which is the same number in both. If you ever see "minus forty" without a unit, the speaker is mostly safe either way.
• Fever and body temperature — Celsius outside the US, Fahrenheit inside. Normal is 37.0 °C / 98.6 °F. Anything above 38.0 °C / 100.4 °F is a fever; above 40.0 °C / 104.0 °F warrants medical attention. The 0.6 °F traditionally cited for "normal" is a 19th-century average that overstates how warm modern bodies actually run; recent research puts the typical baseline closer to 36.6 °C / 97.9 °F.
• Physics and chemistry — Kelvin almost always, because the equations work cleanly with absolute temperature. The ideal gas law, blackbody radiation, the Stefan-Boltzmann law, and reaction rate calculations all want Kelvin inputs. Plugging in a negative Celsius number gives wrong answers fast.
• Astronomy — Kelvin for star surface temperatures (the Sun is about 5,773 K, a red dwarf is about 3,500 K, a blue giant might be 30,000 K). Celsius and Fahrenheit aren't used because the numbers would be unwieldy.
• HVAC and home thermostats — whichever scale the country uses. Comfortable indoor temperature is 20–22 °C / 68–72 °F.

Most temperature-converter pages assume you only want C to F, or only mention Kelvin in a footnote. Big software either bundles temperature into a 200-unit converter behind a sign-up wall, or it's a single-shot Google answer with no decimals. This page is just the three scales, kept live and copy-able.

Related conversions

Temperature rarely shows up alone in real work. A few neighbors worth knowing about:

• Length Converter — meters, feet, inches, miles, and the rest. The other half of recipe and engineering conversion.
• Weight Converter — grams, kilograms, ounces, pounds. Pairs with temperature for cooking and shipping calculations.
• mL to fl oz Converter — volume conversion, with a built-in cooking measurement table.
• Density Calculator — uses temperature as an input because the density of water (and most materials) changes with how warm or cold it is.
• Dew Point Calculator — combines temperature and humidity to predict condensation; useful for weather, HVAC, and avoiding mold.
• Heat Index Calculator — the "feels like" temperature, which factors in humidity to estimate how hot the air actually feels on skin.

Frequently asked questions

What's the easiest way to estimate Celsius to Fahrenheit in my head?

Double the Celsius number and add 30. So 20 °C becomes roughly 70 °F (the exact answer is 68). It's off by a few degrees at the extremes, but for "is it sweater weather?" the approximation is good enough. The exact formula is F = C × 1.8 + 32; the double-and-add-30 trick uses 2 and 30 instead of 1.8 and 32, which is why it drifts at high and low temperatures.

What temperature is the same in Celsius and Fahrenheit?

−40. Set C = F in the conversion equation and solve: F = 9/5 × F + 32 gives F = −40. It's the only crossover point. If you ever see a weather report mentioning "minus forty" without specifying the scale, both readings agree, so the omission is harmless.

Is body temperature really 98.6 °F?

It's the traditional figure, taken from a 19th-century study of 25,000 patients. More recent work suggests the average modern body temperature is closer to 36.6 °C / 97.9 °F, and that individual baselines vary by 0.5 °C / 1 °F in either direction depending on age, time of day, and menstrual cycle. A fever is still defined as anything above 38.0 °C / 100.4 °F regardless of where your personal baseline sits.

Why does cooking sometimes use °C, sometimes °F, sometimes "gas mark"?

American recipes default to Fahrenheit. European recipes default to Celsius. British recipes sometimes use "gas mark," an old UK system where Mark 1 is roughly 135 °C / 275 °F and each mark up adds about 14 °C / 25 °F. The Temperature Converter handles C and F directly; for gas marks, Mark 4 is the equivalent of 180 °C / 350 °F (a moderate oven for cakes), and most recipes that use gas marks include a Celsius equivalent in parentheses.

Why is Kelvin written without a degree symbol?

Convention. Celsius and Fahrenheit use "°C" and "°F" because they're relative scales — the degree mark refers to the divisions between two reference points. Kelvin is absolute, so writing "300 K" is treated more like writing "300 meters." It's a small typographic choice that signals the underlying physics: Kelvin measures total thermal energy, not distance from an arbitrary zero.

What's the hottest temperature physically possible?

There's no agreed-upon upper limit the way absolute zero is a lower limit. The current speculative ceiling is the Planck temperature, around 1.4 × 10³² K, beyond which the laws of physics as we understand them break down. For practical purposes, the hottest temperatures humans have produced are in particle collider experiments — the Large Hadron Collider has reached around 5 × 10¹² K (5 trillion K) in quark-gluon plasma collisions, briefly hotter than the core of the Sun by a factor of a billion.

Does the converter work offline?

Once the page has loaded, yes. The conversion logic runs entirely in your browser with no server calls. If you lose your connection mid-conversion, the page keeps working. The page itself needs an internet connection only the first time you visit, to download the few kilobytes of HTML and JavaScript that make it run.