Temperature Converter
Convert between Fahrenheit, Celsius, Kelvin, Rankine, and more — instantly. Includes cooking temperatures, body temperature guide, and a real-world reference scale.
Understanding Temperature Scales
Temperature is a measure of the average kinetic energy of the particles in a substance. The scale you use depends on where you are in the world and what you’re measuring — everyday life, scientific research, cooking, and engineering each have their preferred systems.
Fahrenheit (°F)
Developed by Daniel Gabriel Fahrenheit in 1724, this scale set 32°F as the freezing point of water and 212°F as the boiling point at sea level — a range of 180 degrees between these two benchmarks. Fahrenheit originally calibrated his scale using a brine solution (0°F) and human body temperature (96°F, later revised to 98.6°F). The Fahrenheit scale is used primarily in the United States and a few territories for everyday temperature measurement.
Celsius (°C)
Anders Celsius proposed the centigrade scale in 1742. The modern Celsius scale defines 0°C as the freezing point of water and 100°C as the boiling point at standard atmospheric pressure — a clean, intuitive range of 100 degrees. Almost every country in the world uses Celsius for everyday temperatures, and it is the preferred scale in science alongside Kelvin.
💡 Quick Mental Conversions: To convert °F to °C, subtract 32 then divide by 1.8. To convert °C to °F, multiply by 1.8 then add 32. The scales cross at -40° — the only temperature where Fahrenheit and Celsius are equal. A useful rough rule: double the Celsius temperature and add 30 to get a Fahrenheit approximation.
Kelvin (K)
The Kelvin scale is the SI base unit of temperature and is used universally in scientific and engineering contexts. It starts at absolute zero (0 K = -273.15°C = -459.67°F) — the theoretical point at which all particle motion stops. There are no negative Kelvin temperatures. Water freezes at 273.15 K and boils at 373.15 K. Importantly, you say “273 kelvin” not “273 degrees kelvin” — the word “degree” is not used with Kelvin.
Rankine (°R)
The Rankine scale uses absolute zero as its starting point (like Kelvin) but uses Fahrenheit-sized degrees rather than Celsius-sized degrees. 0°R = 0 K = absolute zero. Water freezes at 491.67°R and boils at 671.67°R. Rankine is used in some engineering applications in the United States, particularly in thermodynamics and aerospace engineering that use Imperial units.
The Conversion Formulas
| Convert from | To Celsius | To Fahrenheit | To Kelvin |
|---|
| Celsius (°C) | — | (°C × 9/5) + 32 | °C + 273.15 |
| Fahrenheit (°F) | (°F − 32) × 5/9 | — | (°F + 459.67) × 5/9 |
| Kelvin (K) | K − 273.15 | (K × 9/5) − 459.67 | — |
| Rankine (°R) | (°R − 491.67) × 5/9 | °R − 459.67 | °R × 5/9 |
Why Does the US Still Use Fahrenheit?
The United States is one of only a handful of countries that uses Fahrenheit for everyday temperatures. The metric system (including Celsius) was formally adopted in the US in 1975 through the Metric Conversion Act, but its use was made voluntary, and Fahrenheit persisted in daily life. One argument made for Fahrenheit: the 0–100°F range roughly spans the range of human experience in most inhabited climates, providing intuitive “percent of comfortable range” feedback. Most Americans know instinctively that 90°F is very hot and 20°F is very cold without calculation.
Absolute Zero — The Coldest Possible Temperature
Absolute zero (0 K, -273.15°C, -459.67°F) is the lowest theoretically possible temperature. At this point, atoms have minimum vibrational motion. The third law of thermodynamics states that absolute zero can be approached but never quite reached — it would require infinite energy to remove all thermal energy from a system. Scientists have cooled matter to within a billionth of a degree above absolute zero, but the exact value remains unachievable.
Frequently Asked Questions
What is the formula to convert Celsius to Fahrenheit?
°F = (°C × 9/5) + 32. Or equivalently: multiply by 1.8, then add 32. Example: 20°C → (20 × 1.8) + 32 = 36 + 32 = 68°F. Going the other direction, °C = (°F − 32) × 5/9. Example: 68°F → (68 − 32) × 5/9 = 36 × 0.5556 = 20°C. The two scales are equal at exactly -40° — both -40°C and -40°F are the same temperature.
What is a normal body temperature?
The traditional benchmark of 98.6°F (37°C) is the population average established in 1851 by Carl Wunderlich. However, research published in 2020 found that the average has decreased to about 97.5°F (36.4°C). Normal body temperature varies by individual, time of day (lowest in early morning, highest in late afternoon), age (older adults run slightly lower), and measurement location (oral is 0.5–1°F lower than rectal). A fever is generally defined as above 100.4°F (38°C).
What is absolute zero and can we reach it?
Absolute zero (0 K = -273.15°C = -459.67°F) is the theoretical lowest temperature — the point at which atoms have minimum possible energy. The third law of thermodynamics states it can be approached but never reached. Scientists have cooled atoms to within 38 trillionths of a degree of absolute zero using laser cooling techniques, but the exact value remains physically unachievable.
Why is 350°F the most common oven temperature in recipes?
350°F (177°C) is the sweet spot for most baking — hot enough to cause the Maillard reaction (browning and flavor development) and set starches and proteins, but not so hot that the outside burns before the interior cooks through. It’s the default when a recipe doesn’t specify, producing even results across a wide range of baked goods. Higher temperatures (400–450°F) are used when a crispy exterior is desired, lower (300–325°F) for slow-cooking delicate items or large cuts of meat.
What is the difference between Kelvin and Rankine?
Both Kelvin and Rankine start at absolute zero, making them “absolute” temperature scales with no negative values. The difference is the size of the degree: Kelvin uses Celsius-sized degrees (1 K change = 1°C change), while Rankine uses Fahrenheit-sized degrees (1°R change = 1°F change). To convert: K × 9/5 = °R, or °R × 5/9 = K. Kelvin is universal in science. Rankine is used in some US engineering contexts.
At what temperature does it feel hot vs. cold outside?
Perception of hot and cold is highly subjective and depends on humidity, wind, sunshine, and acclimatization. General benchmarks: below 32°F (0°C) is freezing; 32–50°F (0–10°C) is cold; 50–65°F (10–18°C) is cool; 65–80°F (18–27°C) is comfortable; 80–90°F (27–32°C) is warm to hot; above 90°F (32°C) is hot; above 100°F (38°C) is dangerously hot without hydration and shade. Heat index (combining temperature with humidity) often makes these thresholds feel significantly more intense.
What temperature is used in color temperature for lighting?
Color temperature is measured in Kelvin and describes the hue of light. Warm light (candles, incandescent bulbs) is around 2,700–3,000 K — appearing orange-yellow. Neutral/daylight is 4,000–5,500 K — white. Cool/daylight blue is 6,000–7,000 K. Photography, videography, and interior design use these values to match or set the mood of a space. Despite using Kelvin, color temperature is not the actual physical temperature of anything — it’s a description of how the light appears compared to a theoretical blackbody radiator.