Temperature Converter
Convert between Celsius, Fahrenheit, and Kelvin in an instant. Whether you're adapting a recipe from an American cookbook, interpreting a science paper, or checking if a fever is serious — get an accurate answer without doing the algebra yourself.
Why Temperature Conversion Is Different
Unlike speed or time — where you simply multiply by a fixed ratio — temperature scales have different zero points. Celsius sets 0° at the freezing point of water. Fahrenheit sets 32° at the same point. Kelvin sets 0 at absolute zero, about 273° below water's freezing point. This means every conversion involves both multiplication and an additive offset, which is easy to get wrong by hand.
The converter applies the exact algebraic formulas defined by international metrology standards (BIPM / SI), so you always get the right answer — including at extreme values like cryogenic temperatures or industrial process heat.
The Exact Conversion Formulas
These are the formulas the tool uses. Save them for quick mental estimates when you don't have a converter handy.
°C → °F
(°C × 9/5) + 32Example: 100°C → (100 × 1.8) + 32 = 212°F
°F → °C
(°F − 32) × 5/9Example: 98.6°F → (98.6 − 32) × 0.556 = 37°C
°C → K
°C + 273.15Example: 0°C → 0 + 273.15 = 273.15 K
K → °C
K − 273.15Example: 373.15 K → 373.15 − 273.15 = 100°C
Mental shortcut for °C ↔ °F: Double the Celsius value and add 30 for a quick approximation. It's not exact, but puts you in the right ballpark fast — e.g. 20°C → 20 × 2 + 30 = 70°F (exact: 68°F).
Who Uses This Tool
Home Cooks & Bakers
American recipes use Fahrenheit; European and Australian ovens are labelled in Celsius. A quick conversion means the difference between a perfectly risen loaf and a burnt one.
Travellers & Expats
Weather forecasts in the US use Fahrenheit; most of the world uses Celsius. Knowing that 30°C is a hot day (86°F) helps you pack appropriately.
Students & Researchers
Kelvin is the SI unit for thermodynamic temperature. Physics, chemistry, and engineering problems often require converting from Celsius to Kelvin before plugging into equations.
Healthcare & Parents
Checking whether a temperature reading represents a fever — especially when a thermometer displays a different scale than you're used to.
Engineers & Technicians
Industrial processes, material datasheets, and equipment specs may use any of the three scales depending on origin country. Accurate conversion is critical.
Developers
APIs and sensor data often return temperatures in Kelvin or Celsius. Quick verification saves time when debugging weather data pipelines or IoT systems.
Landmark Temperature Reference
Anchor points that help you sanity-check any conversion result.
| Temperature | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Dry ice (CO₂) | −78.5 | −109.3 | 194.65 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20–22 | 68–72 | 293–295 |
| Human body (avg) | 37 | 98.6 | 310.15 |
| Water boils (sea level) | 100 | 212 | 373.15 |
| Self-cleaning oven | ~480 | ~900 | ~753 |
| Surface of the Sun | ~5,500 | ~9,900 | ~5,778 |
Oven Temperature Guide
The most common real-world reason people reach for this converter. Gas mark equivalents included for UK recipes.
| Setting | °C | °F | Gas Mark |
|---|---|---|---|
| Very low / warm | 120°C | 250°F | ½ |
| Low | 150°C | 300°F | 2 |
| Moderate | 180°C | 350°F | 4 |
| Moderately hot | 190°C | 375°F | 5 |
| Hot | 220°C | 425°F | 7 |
| Very hot | 240°C | 460°F | 9 |
Fan-assisted ovens typically run 10–20°C hotter than the same setting on a conventional oven. Reduce accordingly.
Worked Examples
Real situations where temperature conversion matters — verify each one with the tool above.
An American recipe calls for a 375°F oven. Your oven dial is in Celsius.
→ (375 − 32) × 5/9 = 190.6°C. Set your oven to 190°C (or Gas Mark 5).
A child has a temperature of 38.5°C. Is that a fever in Fahrenheit?
→ 38.5 × 1.8 + 32 = 101.3°F. Yes — 100.4°F (38°C) and above is the clinical threshold for fever in adults and children.
A chemistry equation needs temperature in Kelvin. Room temperature is 22°C.
→ 22 + 273.15 = 295.15 K. This is the value to plug into equations using the ideal gas law or Boltzmann constant.
A weather app shows 95°F. How hot is that in Celsius?
→ (95 − 32) × 5/9 = 35°C — a very hot summer day. Heat index may feel significantly higher with humidity.
Liquid nitrogen boils at −196°C. What is that in Kelvin and Fahrenheit?
→ K: −196 + 273.15 = 77.15 K. °F: −196 × 1.8 + 32 = −320.8°F.
Tips & Limitations
💡 Tips for best results
- Sanity check with landmarks: 0°C = 32°F and 100°C = 212°F. If your result doesn't make sense relative to these, double-check the direction of the conversion.
- Kelvin is never negative: If you get a negative Kelvin output, the input Celsius value is below −273.15°C, which is physically impossible.
- Fan ovens: Subtract 15–20°C from a conventional recipe temperature when using a convection/fan oven, as they circulate heat more efficiently.
- Body temp varies: 37°C / 98.6°F is an average. Normal range is 36.1–37.2°C (97–99°F) and changes throughout the day.
⚠️ Limitations to know
- Rankine not included: Rankine (°R) is an absolute scale used in some US engineering contexts. It equals Kelvin × 9/5. This tool does not currently include it.
- Oven calibration varies: The oven guide uses standard settings. Real ovens can run 10–25°C above or below the dial setting — an oven thermometer is more reliable than any conversion chart.
- Not for medical diagnosis: The converter gives mathematically accurate results, but interpreting fever or hypothermia always requires clinical judgement from a healthcare professional.
Frequently Asked Questions
How do you convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (or 1.8), then add 32. So 20°C becomes (20 × 1.8) + 32 = 68°F. The tool does this for you instantly, including for decimal inputs.
How do you convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5/9 (≈ 0.5556). So 98.6°F becomes (98.6 − 32) × 5/9 = 37°C — normal body temperature.
At what temperature are Celsius and Fahrenheit equal?
They cross at exactly −40°. Both −40°C and −40°F represent the same temperature — the only point where the two scales agree. You can verify this with the tool: enter −40 in either field.
Why doesn't Kelvin use a degree symbol?
Because Kelvin is an absolute scale with a fixed, physically meaningful zero point (absolute zero), it is treated as a unit of measurement, not a position on a relative scale. The 2019 revision to the SI system formally removed the degree symbol from Kelvin, reflecting that it measures thermodynamic temperature directly rather than as a degree offset.
What is absolute zero and can it be reached?
Absolute zero (0 K / −273.15°C) is the temperature at which matter has minimum thermodynamic energy. The third law of thermodynamics says it cannot be reached in a finite number of steps — but scientists have cooled matter to within billionths of a Kelvin of it in laboratory settings.
Does the converter work for negative temperatures?
Yes. Negative Celsius and Fahrenheit values are fully supported. The only physical constraint is that Kelvin cannot be negative — the tool will reflect this correctly if you enter a Celsius value below −273.15°C.
How the Converter Works
Temperature conversion is not a simple ratio — it requires both scaling and shifting because each scale has a different zero point. The converter applies the exact BIPM-defined formulas for each direction: Celsius is used as the internal pivot, with Fahrenheit and Kelvin derived from it in a single step per output field.
All arithmetic runs in JavaScript's 64-bit double-precision floating-point environment, giving at least 15 significant digits of accuracy — more than sufficient for any practical use, from cooking to cryogenics. No values are sent to a server; the calculation is entirely local to your browser.