Temperature Converter
25°C equals 77°F, and 0°C equals 32°F. A temperature converter turns a reading in Celsius, Fahrenheit, or Kelvin into the equivalent value on a different scale. Enter a value, choose the source scale, choose the target scale, and the tool applies the correct temperature equation instead of a plain multiplication factor. Temperature scales do not share a common zero point, so an accurate conversion needs both a multiplication step and an addition or subtraction step, unlike converting a length or a weight. This temperature converter is useful for reading a weather forecast from another country, following a recipe written in Fahrenheit while your oven only displays Celsius, checking a lab reading in Kelvin, or converting a thermostat setting, travel packing list, or classroom worksheet from one scale to another without doing the arithmetic by hand.
Quick answer
Celsius to Fahrenheit multiplies by 9/5 (or 1.8) and adds 32. For example, 25°C is (25 x 9/5) + 32 = 77°F.
What this tells you
- •Celsius to Fahrenheit multiplies by 9/5 (or 1.8) and adds 32. For example, 25°C is (25 x 9/5) + 32 = 77°F.
- •Fahrenheit to Celsius subtracts 32 first, then multiplies by 5/9. For example, 98.6°F is (98.6 - 32) x 5/9 = 37°C.
- •Kelvin never goes negative because 0 K is absolute zero. Convert Kelvin to Celsius by subtracting 273.15, and convert back by adding 273.15.
- •-40 is the one point where Celsius and Fahrenheit show the same number, since (-40 x 9/5) + 32 = -40.
- •The converter rounds the number shown on screen, but the calculation itself always runs on the full, unrounded formula.
How to Use
- 1Enter the temperature value you want to convert. Positive numbers, negative numbers, and decimals are all supported.
- 2Select the source scale (Celsius, Fahrenheit, or Kelvin) that matches your starting reading.
- 3Select the target scale you want the value converted into.
- 4Click Calculate to see the converted temperature, along with the source scale, target scale, and the conversion formula used.
- 5Check the sign on negative values carefully. Fahrenheit and Celsius negative ranges do not match up until you reach -40, so a small input mistake can flip a result from cold to mild.
How It Works
Formula
Celsius to Fahrenheit: F = (C x 9/5) + 32. Fahrenheit to Celsius: C = (F - 32) x 5/9. Celsius to Kelvin: K = C + 273.15.This temperature converter treats Celsius as the base scale. For a Fahrenheit or Kelvin starting value, it first converts to Celsius, then converts from Celsius to whatever target scale you picked. Converting Celsius to Fahrenheit multiplies by 9/5 and adds 32, because each Fahrenheit degree is smaller than a Celsius degree and the two scales start counting from different zero points (0°C is 32°F). Converting to Kelvin only needs addition, since a Kelvin degree is the same size as a Celsius degree and the scales differ only by a fixed 273.15 offset, which is absolute zero expressed in Celsius. Because temperature formulas mix multiplication with addition or subtraction, you cannot convert temperature with a single ratio the way you can convert length, weight, or volume.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Celsius to Fahrenheit: comfortable room temperature
Multiply 25 by 9/5 to get 45, then add 32 for a result of 77°F. This is a common comparison when a thermostat or weather app displays Celsius but you think in Fahrenheit.
Fahrenheit to Celsius: normal body temperature
Subtract 32 from 98.6 to get 66.6, then multiply by 5/9 for exactly 37°C. This is the figure most commonly cited as average human body temperature on the Celsius scale.
Celsius to Fahrenheit: oven baking temperature
Multiply 180 by 9/5 to get 324, then add 32 for 356°F. Recipes written for European ovens often list Celsius settings that need converting for US-style Fahrenheit dials.
Fahrenheit to Celsius: a hot summer day
Subtract 32 from 100 to get 68, then multiply by 5/9 for 37.777...°C, which rounds to 37.78°C. Many heat-advisory thresholds in Fahrenheit-based forecasts sit near this range.
Celsius to Kelvin: the freezing point of water
Kelvin conversion is addition only, so 0°C plus the 273.15 offset gives 273.15 K. This value anchors the Kelvin scale and shows why Kelvin has no negative readings for ordinary weather.
Fahrenheit to Celsius: a US recipe in a Celsius oven
Marco's roasted vegetable recipe from a US site says 425 F, and his oven dial is marked in Celsius. Subtract 32 to get 393, multiply by 5/9, and the converter returns 218.333... C, shown as 218.33. Oven dials step in 10s, so he sets 220 C, which is 428 F and close enough that the extra 3 F makes no difference to the roast. The same reading in kelvin is 491.48 K, which nobody needs for dinner but shows the Celsius-plus-273.15 step.
Kelvin to Celsius: a lab notebook reading
Subtract the 273.15 offset from 310.15 K to get 37°C, the same body-temperature figure from the Fahrenheit example above. Lab equipment and scientific papers often report readings in Kelvin, so this conversion is common when checking a result against a Celsius or Fahrenheit reference.
Landmark temperatures on all three scales
Reference points people convert most often, from absolute zero to a hot oven, shown the way the converter reports them.
| Landmark | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | -273.15 C | -459.67 F | 0 K |
| Celsius and Fahrenheit agree | -40 C | -40 F | 233.15 K |
| Household freezer setting | -18 C | -0.4 F | 255.15 K |
| Water freezes (standard pressure) | 0 C | 32 F | 273.15 K |
| Refrigerator setting | 4 C | 39.2 F | 277.15 K |
| Room temperature | 20 C | 68 F | 293.15 K |
| Human body, textbook average | 37 C | 98.6 F | 310.15 K |
| Water boils (one standard atmosphere) | 100 C | 212 F | 373.15 K |
| Slow oven | 150 C | 302 F | 423.15 K |
| Moderate oven | 180 C | 356 F | 453.15 K |
| Hot oven | 200 C | 392 F | 473.15 K |
| Very hot oven | 220 C | 428 F | 493.15 K |
Computed with the formula above from the Celsius value in each row, except absolute zero, which starts from 0 K. The fixed points are the scale definitions: 32 F and 212 F for freezing and boiling water at one standard atmosphere, and 0 C = 273.15 K per the SI Brochure (9th edition) and NIST. The oven labels and the freezer and refrigerator settings are common cookbook and appliance conventions, not standards.
Where the three scales come from, and what the converter leaves out
Fahrenheit and Celsius are both anchored to water. Fahrenheit puts freezing at 32 and boiling at 212 at one standard atmosphere, which leaves 180 degrees between them. Celsius puts the same two points at 0 and 100, leaving 100 degrees. That is where the 9/5 comes from: 180 divided by 100. NIST's SI temperature page states the rest of the relationship in one line, one Celsius degree is an interval of 1 K and of 1.8 Fahrenheit degrees, and 0 C sits at 273.15 K. Every conversion on this page is those two facts rearranged.
The kelvin is defined differently from the other two. Since 20 May 2019, the SI Brochure (9th edition) defines it by fixing the Boltzmann constant at 1.380 649 x 10 to the minus 23 joules per kelvin, so a kelvin is a fixed amount of thermal energy rather than a fraction of the distance between two water points. Before 2019 the kelvin was defined by the triple point of water at exactly 273.16 K. The redefinition did not move the 273.15 offset the converter uses, and it did not change the size of a degree, so a conversion done in 2010 and one done today give the same number.
Real thermometers are not calibrated against the Boltzmann constant directly. Laboratories use the International Temperature Scale of 1990 (ITS-90), adopted by the CIPM in 1989, which fixes a set of reproducible points such as the triple point of water and specifies how to interpolate between them with platinum resistance thermometers and other instruments. ITS-90 approximates thermodynamic temperature closely, and the small known differences are why metrologists distinguish a temperature on ITS-90 from a thermodynamic one. For weather, cooking, and body temperature the difference is far below anything a household thermometer can show.
The converter does arithmetic on a number you type, and the limits follow from that. The 212 F and 100 C boiling point only holds at one standard atmosphere, and water boils a few degrees lower at mountain altitudes. The 98.6 F body-temperature figure is a 19th-century population average that later studies have put slightly lower, so a healthy reading a few tenths under it is normal. Display rounding is the other thing to watch: the formula keeps full precision and the on-screen value is rounded, so chain conversions should start from the original reading rather than from a rounded result.
Common mistakes
- Applying only a multiplication factor. Temperature scales are not a simple ratio like inches to centimeters, so skipping the +32/-32 step or the 273.15 offset produces a value that looks close but is wrong.
- Doing the steps out of order for Fahrenheit to Celsius. Subtract 32 first, then multiply by 5/9. Multiplying first and subtracting 32 afterward gives a different, incorrect number.
- Assuming a Kelvin result can be negative. Kelvin has no negative values because 0 K is absolute zero, the coldest temperature physically possible, so a negative Kelvin output usually means the wrong source scale was selected.
- Forgetting the -40 crossover point. Celsius and Fahrenheit only match at -40, so assumptions about which scale reads higher near freezing do not hold for extreme cold readings.
- Rounding an intermediate step before finishing the calculation. Rounding partway through a Fahrenheit-to-Celsius or Celsius-to-Kelvin conversion compounds a small error, which matters if the rounded figure feeds into another calculation.
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