Temperature Converter

Quick Reference Table

Celsius (°C)	Fahrenheit (°F)	Kelvin (K)	Description
-273.15	-459.67	0	Absolute Zero
-40	-40	233.15	C = F point
0	32	273.15	Water freezes
20	68	293.15	Room temperature
37	98.6	310.15	Body temperature
100	212	373.15	Water boils

Conversion Formulas

Understanding Temperature Scales

Celsius (°C) - Metric Scale

Definition: Water freezes at 0°C and boils at 100°C at standard atmospheric pressure. One degree Celsius equals one kelvin in magnitude.

History: Developed by Swedish astronomer Anders Celsius in 1742. Originally inverted (0 was boiling, 100 was freezing), it was reversed after his death. Named "centigrade" until 1948 when officially renamed Celsius.

Current Use: Used worldwide as the standard temperature scale except in the United States. Official scale in nearly all countries for weather forecasts, cooking, science, and daily life. Used in medical settings globally for body temperature.

Fahrenheit (°F) - Imperial Scale

Definition: Water freezes at 32°F and boils at 212°F at standard pressure. One degree Fahrenheit equals 5/9 of a kelvin or degree Celsius.

History: Created by German physicist Daniel Gabriel Fahrenheit in 1724. Originally based on three reference points: the coldest temperature achievable with ice/salt mixture (0°F), water freezing (32°F), and human body temperature (originally 96°F, later adjusted to 98.6°F).

Current Use: Primary temperature scale in the United States, Cayman Islands, Palau, Bahamas, and Liberia. Used for weather reports, cooking, and everyday temperatures in these regions. Provides finer granularity for common temperatures compared to Celsius.

Kelvin (K) - Absolute Scale

Definition: The SI base unit of temperature. Zero kelvin (0 K) is absolute zero, the theoretical lowest possible temperature. Water freezes at 273.15 K and boils at 373.15 K. Note: No degree symbol is used with Kelvin.

History: Proposed by William Thomson (Lord Kelvin) in 1848. Based on the Carnot cycle and absolute thermodynamic temperature. Since 2019, defined by setting the Boltzmann constant to exactly 1.380649 × 10⁻²³ J/K.

Current Use: Primary scale in physical sciences, especially thermodynamics, physics, and chemistry. Used for very high and very low temperatures, scientific research, and equations where absolute temperature is required. Essential for gas laws and quantum mechanics.

Rankine (°R) - Absolute Imperial Scale

Definition: An absolute temperature scale using Fahrenheit-sized degrees. Absolute zero is 0°R (−459.67°F). Water freezes at 491.67°R and boils at 671.67°R.

History: Named after Scottish engineer William Rankine who proposed it in 1859. Created as an absolute scale analogous to Kelvin but using Fahrenheit degree increments.

Current Use: Rarely used today. Occasionally appears in some US engineering fields, particularly thermodynamics and heat transfer calculations. Largely replaced by Kelvin even in countries using Fahrenheit.

Common Temperature Comparisons

• Absolute Zero: -273.15°C / -459.67°F / 0 K (lowest possible temperature)
• Coldest recorded on Earth: -89.2°C / -128.6°F (Antarctica, 1983)
• Dry ice sublimes: -78.5°C / -109.3°F
• Average winter day: 0°C / 32°F
• Comfortable room temp: 20-22°C / 68-72°F
• Human body: 37°C / 98.6°F
• Hot summer day: 35°C / 95°F
• Baking oven: 180-200°C / 350-400°F
• Surface of the Sun: ~5,500°C / ~10,000°F

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?

Multiply the Celsius temperature by 9/5 (or 1.8) and add 32. Formula: °F = (°C × 9/5) + 32. Example: 25°C × 1.8 + 32 = 77°F. Quick tip: 0°C = 32°F, and each degree Celsius equals 1.8 degrees Fahrenheit.

How do I convert Fahrenheit to Celsius?

Subtract 32 from the Fahrenheit temperature, then multiply by 5/9 (or divide by 1.8). Formula: °C = (°F - 32) × 5/9. Example: 77°F - 32 = 45, then 45 ÷ 1.8 = 25°C.

What temperature is the same in Celsius and Fahrenheit?

-40 degrees is the same in both scales: -40°C = -40°F. This is the unique point where the two scales intersect.

Why does the US use Fahrenheit?

Historical reasons and cultural inertia. When Fahrenheit was invented (1724), it predated Celsius (1742). By the time the metric system was adopted globally, Fahrenheit was deeply embedded in American infrastructure, education, and culture. Converting would require changing weather services, thermostats, recipes, and education systems.

What is absolute zero?

Absolute zero is the theoretical lowest temperature possible: 0 Kelvin, -273.15°C, or -459.67°F. At this temperature, particles have minimal motion. It's impossible to actually reach, but scientists have gotten within billionths of a degree.

Why doesn't Kelvin use degree symbols?

Kelvin is an absolute scale and is considered a base SI unit, not a relative degree. The SI convention omits the degree symbol (°) for Kelvin. You write "273 K" not "273°K".

Can I use this for cooking temperatures?

Yes! The converter is perfect for converting oven temperatures between Celsius and Fahrenheit. Common conversions: 180°C = 350°F, 200°C = 400°F, 220°C = 425°F.

Common Uses for Temperature Conversion

• Cooking & Baking: Converting recipe oven temperatures between systems
• Travel: Understanding weather forecasts in different countries
• Science & Education: Converting lab data and homework problems
• Medical: Understanding body temperature readings from different thermometers
• HVAC & Engineering: Technical specifications and calculations
• Weather Reports: Understanding international climate data
• Manufacturing: Material processing and quality control

Tips for Accurate Conversions

1. Always use precise formulas for scientific work
2. Round appropriately for your application (cooking vs. lab work)
3. Remember that Celsius and Fahrenheit have different zero points
4. Kelvin never goes negative (absolute scale)
5. For quick estimates: C to F multiply by 2 and add 30 (approximate)
6. Verify oven temperatures with an oven thermometer for accuracy