CelsiusFahrenheitKelvinRankineAll Scales at OnceFree
Temperature Converter
Convert instantly between all four major temperature scales — Celsius, Fahrenheit, Kelvin, and Rankine. Results update in real time, showing all four scales simultaneously so you can cross-reference cooking temperatures, medical ranges, scientific values, and engineering specifications in one view. Uses the exact mathematical definitions: K = °C + 273.15 and °F = (°C × 9/5) + 32, ensuring precision across all conversions.
International standard (SI derived)
Everyday use — United States
Scientific / thermodynamics — SI base
Engineering thermodynamics (US)
Historical — 18th-century Russia
Historical — proposed by Isaac Newton
Historical — European dairy industry
Historical — Danish scale (pre-Celsius)
Reference Points
| Reference | °C | °F | K | °R | °De | °N | °Ré | °Rø |
|---|---|---|---|---|---|---|---|---|
| Absolute Zero | -273.15 | -459.67 | 0 | 0 | 559.725 | -90.1395 | -218.52 | -135.90375 |
| Water Freezing | 0 | 32 | 273.15 | 491.67 | 150 | 0 | 0 | 7.5 |
| Room Temperature | 22 | 71.6 | 295.15 | 531.27 | 117 | 7.26 | 17.6 | 19.05 |
| Normal Body Temp | 37 | 98.6 | 310.15 | 558.27 | 94.5 | 12.21 | 29.6 | 26.925 |
| Water Boiling | 100 | 212 | 373.15 | 671.67 | 0 | 33 | 80 | 60 |
| Sun Surface | 5505 | 9941 | 5778.15 | 10400.67 | -8107.5 | 1816.65 | 4404 | 2897.625 |
Click any row to load that reference point into the converter.
Industry & Science Context
- Celsius (°C) — The international standard for everyday temperature. Used by 195+ countries. 0°C = water freezes, 100°C = water boils at sea level.
- Fahrenheit (°F) — Standard in the United States. Human body temperature (98.6°F) and key weather benchmarks are well-represented on this scale.
- Kelvin (K) — The SI base unit of thermodynamic temperature. 0 K = absolute zero, the coldest possible temperature. Critical in physics, chemistry, and astronomy. Note: no degree symbol.
- Rankine (°R) — Absolute temperature scale using Fahrenheit degrees. Used in some US engineering fields (thermodynamics, aerospace). 0°R = absolute zero.
- Delisle, Newton, Réaumur, Rømer — Historical scales from the 1700s. Réaumur (°Ré) was once widely used in France and Germany, particularly in food/dairy contexts. All are now obsolete in practice.
- −40° — The unique crossover point where Celsius and Fahrenheit are equal: −40°C = −40°F.
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Real-Time
All 4 scales update instantly as you type
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Exact Formulas
Uses the official SI definition for each scale
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Private
All calculations run locally in your browser
Key Temperature Reference Points
| Reference Point | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
| Oven (moderate) | 180 | 356 | 453.15 |
Frequently Asked Questions
Is this temperature converter free to use?
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Yes, the RoughTools Temperature Converter is completely free with no account, subscription, or payment required. You can convert between Celsius, Fahrenheit, Kelvin, and Rankine as many times as needed at no cost. RoughTools is funded through non-intrusive advertising, keeping every converter permanently free. There are no usage limits, no premium scales behind a paywall, and no registration of any kind required to use the full converter.
Do I need to sign up to convert temperatures?
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No account, email address, or registration is required. Enter a temperature value and the converter instantly shows the equivalent in all other supported scales simultaneously. There is no login wall and no data stored about your conversions. The converter is entirely anonymous — your temperature lookups remain completely private, whether you are checking a fever, calibrating an oven, or working on a thermodynamics problem.
Does this tool store the temperature values I enter?
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No. All conversions run entirely within your browser using JavaScript. The values you enter are never transmitted to RoughTools servers, never logged, and never shared with any third party. Once you close the browser tab, all data is gone. Your calculations remain completely private throughout every session.
Does the temperature converter work on mobile and tablet?
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Yes, the converter is fully responsive and works on all modern smartphones and tablets. All input fields and the multi-scale results display are optimised for touch screens. This is useful when following a recipe that uses a different temperature scale, checking medical temperature references, or looking up industrial process temperatures on the go from your phone or tablet.
Which browsers support this temperature converter?
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The Temperature Converter works in all modern browsers: Google Chrome, Mozilla Firefox, Microsoft Edge, Safari, Opera, and Brave on both desktop and mobile. No plugins or extensions are required. The converter uses standard JavaScript arithmetic that runs natively in every current browser. Any current version of Chrome, Firefox, or Safari on desktop or mobile is fully supported.
How accurate are the temperature conversions?
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The conversions use the exact mathematical formulas defined by the International System of Units. The relationship between Celsius and Kelvin is exact: K = °C + 273.15. The Fahrenheit conversion is exact: °F = °C × (9/5) + 32. Rankine is defined as °R = °F + 459.67. All conversions are mathematically precise to the limits of standard floating-point arithmetic, providing accuracy far beyond any practical measurement requirement.
Can I use this temperature converter offline?
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Once the page has fully loaded in your browser, all conversions run in JavaScript without requiring an active internet connection. You can enter temperatures and see all scale conversions offline after the initial page load. This is useful when reviewing lab data, working in the kitchen, or checking process temperatures in locations with poor connectivity. The initial page load requires internet access, but after that the converter functions entirely client-side.
How do I convert a temperature step by step?
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To convert a temperature: (1) Enter the numeric value in the input field. (2) Select the source scale — Celsius, Fahrenheit, Kelvin, or Rankine. (3) The results panel instantly shows the equivalent value in all three other scales simultaneously. Results update in real time as you type, so there is no need to press a calculate button. You can read off all four scales at once, which is especially useful when working across metric and imperial contexts.
Why should I use RoughTools instead of a search engine for temperature conversion?
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Search engines convert between one pair of temperature scales at a time. RoughTools Temperature Converter shows all four scales simultaneously in a single view — enter a value in any scale and immediately see all others updated. This is far more efficient when you need to cross-reference Celsius, Fahrenheit, and Kelvin at the same time, such as when reading scientific literature that uses Kelvin alongside everyday references that use Celsius or Fahrenheit.
How do I report a bug or request a new temperature scale?
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To report a bug or request an additional scale — such as Delisle, Newton, Réaumur, or Rømer — use the feedback link in the site footer or visit the RoughTools contact page. When reporting a bug, include the input value and scale you selected, the browser and OS, and the incorrect result versus what you expected. Feature requests are reviewed and prioritised regularly by the development team.
How do I convert Celsius to Fahrenheit manually?
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The formula is: °F = (°C × 9/5) + 32. For example, 100°C × 1.8 + 32 = 212°F (boiling point of water). For quick mental estimation, double the Celsius temperature and add 30 — this gives an approximate Fahrenheit value within a few degrees for typical everyday temperatures. For example, 20°C → 20 × 2 + 30 = 70°F (actual is 68°F). The reverse formula is: °C = (°F − 32) × 5/9.
What is absolute zero and why does it matter?
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Absolute zero is the lowest possible temperature — the point at which all molecular and atomic motion ceases. It equals 0 Kelvin, −273.15°C, or −459.67°F. No temperature below absolute zero can exist. The Kelvin scale starts at absolute zero specifically so that thermodynamic calculations work cleanly — doubling the Kelvin temperature truly doubles the thermal energy of a system. Scientists use Kelvin for this reason: 200 K has exactly twice the thermal energy of 100 K, whereas you cannot say the same about 200°C versus 100°C.
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