Temperature Converter
Convert temperatures between Celsius, Fahrenheit, Kelvin, and Rankine instantly. Use our free online temperature converter for weather, cooking, and scientific calculations.
Understanding Temperature Scales
Temperature measures the average kinetic energy of particles in a substance. Different regions and fields use different temperature scales. Celsius dominates global everyday use, Fahrenheit remains common in the US, and Kelvin serves scientific applications.
Anders Celsius created his scale in 1742, setting water's freezing point at 0° and boiling point at 100°. Daniel Fahrenheit developed his scale in 1724, using a brine mixture for 0° and human body temperature for 96° (later adjusted to 98.6°). William Thomson (Lord Kelvin) introduced the absolute Kelvin scale in 1848, starting at absolute zero.
Temperature Conversion Formulas
Celsius to Fahrenheit
°F = (°C × 9/5) + 32
Example: 25°C × 9/5 + 32 = 77°F
Fahrenheit to Celsius
°C = (°F - 32) × 5/9
Example: (77°F - 32) × 5/9 = 25°C
Celsius to Kelvin
K = °C + 273.15
Example: 25°C + 273.15 = 298.15 K
Kelvin to Celsius
°C = K - 273.15
Example: 300 K - 273.15 = 26.85°C
Fahrenheit to Rankine
°R = °F + 459.67
Example: 77°F + 459.67 = 536.67°R
Kelvin to Rankine
°R = K × 9/5
Example: 300 K × 9/5 = 540°R
Common Temperature Conversions
| Celsius | Fahrenheit | Kelvin | Description |
|---|---|---|---|
| 0°C | 32°F | 273.15 K | Water freezes |
| 10°C | 50°F | 283.15 K | Cool day |
| 20°C | 68°F | 293.15 K | Room temperature |
| 25°C | 77°F | 298.15 K | Warm day |
| 37°C | 98.6°F | 310.15 K | Body temperature |
| 100°C | 212°F | 373.15 K | Water boils |
Oven Temperature Guide
| Setting | Celsius | Fahrenheit | Best For |
|---|---|---|---|
| Cool | 120-140°C | 250-285°F | Slow cooking, dehydrating |
| Very Low | 140-150°C | 285-300°F | Slow roasting |
| Low | 150-160°C | 300-325°F | Cakes, delicate baking |
| Moderate | 160-180°C | 325-350°F | Most baking, roasting |
| Moderately Hot | 180-190°C | 350-375°F | Cookies, breads |
| Hot | 190-220°C | 375-425°F | Pizza, high-heat roasting |
| Very Hot | 220-260°C | 425-500°F | Searing, broiling |
Weather Temperature Reference
| Celsius | Fahrenheit | Conditions |
|---|---|---|
| -20°C | -4°F | Extremely cold, dangerous exposure |
| -10°C | 14°F | Very cold, heavy winter clothing needed |
| 0°C | 32°F | Freezing, ice forms |
| 10°C | 50°F | Cool, light jacket needed |
| 20°C | 68°F | Comfortable, light clothing |
| 30°C | 86°F | Warm, summer weather |
| 40°C | 104°F | Hot, heat advisory possible |
Temperature Scale Comparison
| Reference Point | Celsius | Fahrenheit | Kelvin | Rankine |
|---|---|---|---|---|
| Absolute Zero | -273.15°C | -459.67°F | 0 K | 0°R |
| Water Freezes | 0°C | 32°F | 273.15 K | 491.67°R |
| Human Body | 37°C | 98.6°F | 310.15 K | 558.27°R |
| Water Boils | 100°C | 212°F | 373.15 K | 671.67°R |
When to Use Each Temperature Scale
Everyday Use
Weather forecasts, cooking, body temperature (most countries)
Science
General laboratory work, chemistry, biology
Industry
Manufacturing, HVAC, food processing (global)
Everyday Use
Weather, cooking, body temperature (US only)
HVAC
Home thermostats, air conditioning (US)
Cooking
Oven temperatures, meat thermometers (US)
Physics
Thermodynamics, quantum mechanics, astrophysics
Chemistry
Gas laws, reaction rates, absolute measurements
Engineering
Cryogenics, high-temperature processes
Engineering
Thermodynamics (US engineering fields)
Aerospace
Some US aerospace applications
HVAC
Specialized US heating/cooling calculations
Quick Mental Conversion Tips
Celsius to Fahrenheit (Approximate)
Double the Celsius temperature and add 30. Example: 20°C × 2 = 40 + 30 = 70°F (actual: 68°F). This works well for typical weather temperatures.
Fahrenheit to Celsius (Approximate)
Subtract 30 from Fahrenheit and divide by 2. Example: 70°F - 30 = 40 ÷ 2 = 20°C (actual: 21.1°C). Good enough for weather estimates.
Key Reference Points
Memorize these: 0°C = 32°F (freezing), 10°C = 50°F (cool), 20°C = 68°F (comfortable), 30°C = 86°F (warm), 40°C = 104°F (hot). Use these to estimate other temperatures.
Frequently Asked Questions
At what temperature are Celsius and Fahrenheit equal?
Celsius and Fahrenheit scales intersect at -40 degrees. -40°C equals -40°F. This occurs because the scales have different zero points and different degree sizes.
Why does the US still use Fahrenheit?
The US adopted Fahrenheit before the metric system gained global acceptance. Changing would require updating countless thermostats, weather services, cookbooks, and public understanding. The cost and effort outweigh perceived benefits.
What is absolute zero?
Absolute zero (0 K, -273.15°C, -459.67°F) represents the lowest possible temperature. At this point, particles have minimal kinetic energy. Scientists have cooled matter to within billionths of a degree above absolute zero.
Is Kelvin written with a degree symbol?
No. Kelvin uses just "K" without a degree symbol. This distinguishes it as an absolute scale starting at zero. Celsius and Fahrenheit use degree symbols (°C, °F) because their zero points are arbitrary.
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