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Temperature Converter

Convert temperature between Fahrenheit, Celsius, Kelvin, and Rankine with formula display and reference points.

Thermal Converter

22.2222

Converted Temperature

22.2222
°C
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What is Temperature Scales: Fahrenheit, Celsius & Kelvin?

The three major temperature scales, why Kelvin is the only 'absolute' scale with a true zero, and the exact formulas that convert between them.

Mathematical Foundation

Celsius ↔ Fahrenheit Conversion
°F=95⋅°C+32\degree F = \frac{9}{5} \cdot \degree C + 32
9/59/5= The ratio of Fahrenheit degrees to Celsius degrees per unit change (1°C = 1.8°F)
+32+32= The offset — water freezes at 32°F vs 0°C

Laws & Principles

  • Absolute Zero & Kelvin: Kelvin is the SI base unit of temperature. 0 K = -273.15°C is 'absolute zero' — the theoretical minimum temperature where molecular motion completely ceases. It is physically impossible to reach 0 K (third law of thermodynamics). Kelvin uses the same degree interval as Celsius, so a change of 1 K = a change of 1°C. To convert: K = °C + 273.15.
  • Why Fahrenheit Uses 32: Daniel Fahrenheit (1724) set 0°F as the coldest temperature he could produce (salt-ice mixture) and 96°F as approximate human body temperature. This 'natural' anchoring created the 32°F freezing point and 212°F boiling point of water. The 180°F span between these two points is deliberately divisible by many small integers, making arithmetic easier for pre-calculator tradespeople.

Step-by-Step Example Walkthrough

" Converting normal body temperature of 98.6°F to Celsius and Kelvin. "

  1. °C = (98.6 - 32) × 5/9 = 66.6 × 0.5556 = 37.0°C.
  2. K = 37.0 + 273.15 = 310.15 K.
Final Result: 98.6°F = 37.0°C = 310.15 K

Quick Answer: Temperature Conversion Formulas

°F to °C: (°F − 32) × 5/9. °C to °F: (°C × 9/5) + 32. °C to K: °C + 273.15. Key crossover: -40° is the same in both °F and °C. Body temp: 98.6°F = 37°C. Water boils: 212°F = 100°C. Water freezes: 32°F = 0°C.

Temperature Reference Points

Reference°F°CK
Absolute Zero-459.67-273.150
F/C Crossover-40-40233.15
Water Freezes320273.15
Body Temperature98.637.0310.15
Water Boils212100373.15

Water boiling point varies with altitude. At 5,000 ft elevation, water boils at 203°F (95°C). At 10,000 ft: 194°F (90°C). This affects cooking times significantly.

Frequently Asked Questions

What is Kelvin and why does science use it?

Kelvin starts at absolute zero — the coldest possible temperature where all molecular motion stops. This makes it an absolute scale: 200K is exactly twice as hot as 100K in terms of thermal energy. Celsius and Fahrenheit can't make that claim because their zeros are arbitrary. Gas laws (PV=nRT), thermodynamics, and radiation physics all require absolute temperature to produce correct results.

Why does the US still use Fahrenheit?

Historical inertia. Fahrenheit was established in the US before the metric system was developed. Interestingly, Fahrenheit has finer resolution for everyday temperatures — the 0-100°F range covers typical weather conditions (-18°C to 38°C), giving more meaningful whole-number distinctions than Celsius for daily life. However, for science, cooking, and global communication, Celsius is far more practical.

How do I quickly estimate °F to °C in my head?

Subtract 30, then divide by 2. This gives a rough estimate within ~2°C for everyday temperatures. Example: 72°F → (72-30)/2 = 21°C (actual: 22.2°C). For °C to °F: double it, add 30. Example: 25°C → (25×2)+30 = 80°F (actual: 77°F). Not exact, but useful for travel and quick mental estimates.

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