Convert Celsius, Fahrenheit, Kelvin and Rankine all at once — with a thermometer showing where your temperature sits.
°C
20
°F
68
Calculator
Converted
68 °F
Kelvin
293.15 K
Rankine
527.67 °R
Celsius
20 °C
Fahrenheit
68 °F
Kelvin
293.15 K
Rankine
527.67 °R
On the thermometer
How temperature conversion works
Every scale shares the same physics, so we convert your value to Celsius first, then out to the others. Fahrenheit uses °F = °C × 9/5 + 32; Kelvin shifts by the exact offset 273.15 (0 °C = 273.15 K); Rankine is the Fahrenheit-degree version of Kelvin, °R = (°C + 273.15) × 9/5.
Celsius and Fahrenheit cross at −40°, the one temperature that reads the same on both. Kelvin and Rankine are absolute scales — they start at absolute zero, the point where molecular motion stops, so they never go negative.
What is the fastest way to convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8) and add 32. For a rough mental estimate, double the Celsius value and add 30 — close enough for weather, though this converter gives the exact figure.
Why does Kelvin not use a degree sign?
Kelvin is an SI base unit measured from absolute zero, so a temperature is written as '300 K', not '300 °K'. Each kelvin is the same size as one Celsius degree.
When is Rankine used?
Rankine (°R) is an absolute scale built on Fahrenheit degrees, common in some US engineering and thermodynamics work where Fahrenheit is the everyday unit but an absolute scale is needed.
Results are estimates. Verify with a professional for important decisions.
About this calculator
Convert any temperature between Celsius, Fahrenheit, Kelvin and Rankine in one step. Type your value, pick the source scale, and all four results update instantly — useful for cooking, science, weather, and engineering.
How to read your results
The four result cards show the equivalent temperature in each scale simultaneously. The visual thermometer marks key reference points — freezing (0 °C / 32 °F), normal body temperature (37 °C / 98.6 °F), boiling (100 °C / 212 °F) and a hot oven — so you can place your value in everyday context.
Worked example
Enter 100 °C (the boiling point of water at sea level) as the input.
The converter returns 212 °F, 373.15 K and 671.67 °R — confirming that water boils at the same physical point on every scale.
Frequently asked questions
What is absolute zero, and why does it matter?
Absolute zero (0 K / −273.15 °C / −459.67 °F) is the lowest possible temperature, where molecular motion effectively stops. Kelvin starts there, making it the natural unit for thermodynamic calculations. No value below 0 K is physically possible.
Why does the United States still use Fahrenheit?
Fahrenheit was the dominant scale in English-speaking countries before Celsius was standardised in the 19th century. The US never adopted the metric system for everyday use, so Fahrenheit persisted in weather forecasts and household contexts, even as science uses Celsius and Kelvin worldwide.
When would I need Rankine?
Rankine (°R) is an absolute scale based on Fahrenheit degrees. It is mainly used in some branches of American engineering thermodynamics — for example, steam tables and aerospace calculations written for US customary units — where an absolute scale is needed but Fahrenheit degree intervals are preferred.
How do I convert Fahrenheit to Celsius mentally?
A quick approximation: subtract 32, then halve the result. For example, 68 °F − 32 = 36 ÷ 2 = 18 °C (exact value is 20 °C, so this is close enough for rough estimates). For exact results, use the formula °C = (°F − 32) × 5/9.
Is there a temperature where Celsius and Fahrenheit are equal?
Yes — at −40 degrees. Both scales read −40 at the same physical temperature, which is a convenient calibration checkpoint often cited in cold-climate discussions.
How it's calculated
All conversions route through Celsius as the internal pivot. From Celsius: Fahrenheit = C × 9/5 + 32; Kelvin = C + 273.15; Rankine = (C + 273.15) × 9/5. To convert from another scale, invert the formula to obtain Celsius first — for example, from Fahrenheit: C = (F − 32) × 5/9; from Kelvin: C = K − 273.15; from Rankine: C = (R − 491.67) × 5/9. Kelvin is the SI base unit for thermodynamic temperature; its zero point is absolute zero. The offsets 273.15 and 491.67 are exact by definition under the International System of Units.
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