🌡️ Temperature Converter

Temperature Conversion Guide

Temperature is the measure of the average kinetic energy of particles in a substance — essentially how hot or cold something is. Three temperature scales are in common use worldwide, each with different reference points and primary applications. Understanding how to convert between them is essential for cooking, weather interpretation, scientific work, and international travel.

The Three Temperature Scales

• Celsius (°C): The metric system temperature scale, used as the everyday standard in nearly every country except the United States. Named after Anders Celsius (1701–1744). Defined with water's freezing point at 0°C and boiling point at 100°C at sea-level atmospheric pressure. Body temperature is approximately 37°C. Comfortable room temperature is 20–22°C.
• Fahrenheit (°F): The traditional scale used for everyday temperatures in the United States. Named after Daniel Gabriel Fahrenheit (1686–1736). Originally set with 0°F at the freezing point of a salt-water solution and 96°F at body temperature. In this scale, water freezes at 32°F and boils at 212°F. Normal body temperature is 98.6°F. Comfortable room temperature is 68–72°F.
• Kelvin (K): The absolute temperature scale used in science and engineering, particularly in physics and chemistry. Named after Lord Kelvin (1824–1907). Starts at absolute zero (0 K), the theoretical temperature at which all molecular motion stops — no colder temperature is physically possible. Kelvin uses the same degree size as Celsius: 1 K difference = 1°C difference. Water freezes at 273.15 K and boils at 373.15 K. Note: Kelvin units are written without a degree symbol (373 K, not 373°K).

Conversion Formulas

• Celsius to Fahrenheit: °F = (°C × 9/5) + 32
• Fahrenheit to Celsius: °C = (°F − 32) × 5/9
• Celsius to Kelvin: K = °C + 273.15
• Kelvin to Celsius: °C = K − 273.15
• Fahrenheit to Kelvin: K = (°F − 32) × 5/9 + 273.15
• Kelvin to Fahrenheit: °F = (K − 273.15) × 9/5 + 32

Mental Shortcuts for Quick Conversions

• Quick °C to °F approximation: Double the Celsius temperature and add 30. This gives a rough answer for everyday weather: 20°C → 20×2+30 = 70°F (actual: 68°F). Excellent for quick mental estimates.
• Quick °F to °C approximation: Subtract 30 from Fahrenheit and divide by 2. 90°F → (90−30)/2 = 30°C (actual: 32.2°C).
• The −40 crossover point: The only temperature that is the same in both Celsius and Fahrenheit is −40°. Below this point, Fahrenheit numbers are higher than Celsius; above it, Fahrenheit numbers are higher.

Key Temperature Reference Points

• Absolute zero: 0 K = −273.15°C = −459.67°F — the coldest possible temperature
• Water freezes: 0°C = 32°F = 273.15 K
• Room temperature: ~20–22°C = 68–72°F = ~293 K
• Normal body temperature: 37°C = 98.6°F = 310.15 K
• Pasteurization: 72°C = 161.6°F (HTST for milk)
• Water boils: 100°C = 212°F = 373.15 K (at sea level)
• Baking oven (moderate): 175°C = 347°F
• Broiling temperature: ~260°C = 500°F
• Surface of the Sun: ~5,500°C = ~9,932°F = ~5,773 K

Practical Applications

• Weather: International travelers must interpret local weather forecasts in Celsius. 30°C is a hot summer day; 10°C is cool jacket weather; 0°C means icy conditions.
• Cooking: Recipe conversions between American (°F) and metric (°C) cookbooks. Oven temperatures vary by recipe origin — a 350°F recipe calls for a 175°C oven setting.
• Medicine: Normal human body temperature is 37°C (98.6°F). A fever is typically defined as above 38°C (100.4°F). Most medical thermometers offer both scales.
• Scientific calculations: Most thermodynamic equations require Kelvin — the ideal gas law (PV = nRT), black-body radiation, and enzyme kinetics all use absolute temperature. Never use Celsius or Fahrenheit in thermodynamic formulas.

Frequently Asked Questions

Why does the U.S. still use Fahrenheit? Historical inertia. The United States adopted Fahrenheit in the colonial era and never underwent the metric transition that most other countries completed in the 20th century. Science, medicine, and aviation in the U.S. use metric units, but everyday weather, cooking, and body temperature remain in Fahrenheit for cultural and economic reasons.

Is there a scale warmer than Fahrenheit? Yes. The Rankine scale is an absolute temperature scale (like Kelvin) but uses Fahrenheit-sized degrees. 0 Rankine = absolute zero; water freezes at 491.67 Rankine. It's used in some U.S. engineering contexts. The Réaumur scale (historical) set water's freezing at 0°Ré and boiling at 80°Ré, but it's now obsolete.

Does water always boil at 100°C? Only at standard atmospheric pressure (101.325 kPa / 14.7 psi, which is sea-level pressure). At high altitude (lower atmospheric pressure), water boils at a lower temperature — in Denver, Colorado (~5,280 ft elevation), water boils at about 95°C (203°F). This affects cooking times, which is why high-altitude recipes adjust boiling times upward.