Kelvin to Celsius Converter
Convert Kelvin to Celsius and Fahrenheit for science, physics and chemistry.
How to use this kelvin to celsius
- Enter a temperature in Kelvin — from a physics problem, chemistry equation, or astrophysics calculation.
- Read Celsius for real-world interpretation of the temperature.
- Check Fahrenheit for US context or comparison with everyday reference points.
- Note: Kelvin cannot be negative — 0 K is absolute zero, the lowest possible temperature.
- For gas law calculations: always convert Celsius to Kelvin before using PV=nRT (add 273.15).
Formula
°C = K − 273.15. °F = °C × 9/5 + 32.
About the Kelvin to Celsius
Kelvin is the SI (International System of Units) base unit for thermodynamic temperature, and it's used throughout physics, chemistry, and astrophysics precisely because it starts at absolute zero. Unlike Celsius or Fahrenheit, where temperatures below zero are common and physically meaningful, a negative Kelvin temperature is mathematically impossible — it would represent less thermal energy than a system with no thermal energy at all. This makes Kelvin uniquely suited for equations and calculations where temperature appears multiplicatively.
The most common engineering and science use of Kelvin is in gas law calculations. The Ideal Gas Law (PV = nRT) requires temperature in Kelvin. Charles's Law (V₁/T₁ = V₂/T₂) requires Kelvin. Gay-Lussac's Law (P₁/T₁ = P₂/T₂) requires Kelvin. Using Celsius in any of these equations produces incorrect results because the zero points are offset. A student who plugs 25°C directly into PV=nRT instead of 298.15 K will get an answer that's off by the ratio 25/298 — about 8.4% error, often enough to fail an exam or misspecify an industrial gas system.
In everyday life, Kelvin appears in two surprising contexts: photography and display technology (color temperature) and astronomy. Camera white balance settings are measured in Kelvin: 2700–3000 K is warm candlelight, 5500–6000 K is daylight, 7000–8000 K is overcast sky. Monitor and TV color temperatures range from 5000–9300 K, where higher K values appear bluer and cooler. The sun's surface is approximately 5,778 K — coincidentally close to standard daylight color temperature, which is why outdoor photography at noon is often considered the most 'neutral' light.
Frequently asked questions
+What is 0 Kelvin in Celsius and Fahrenheit?
0 K = −273.15°C = −459.67°F — absolute zero. This is the theoretical minimum temperature where all molecular motion stops. Absolute zero has never been achieved in practice; the coldest temperatures achieved in laboratory conditions are within billionths of a kelvin above absolute zero. The coldest natural temperature in the universe (outside of lab conditions) is approximately 2.7 K — the cosmic microwave background radiation.
+What is room temperature in Kelvin?
Standard room temperature is approximately 293–298 K (20–25°C). In chemistry and physics, 'standard temperature' is defined as exactly 273.15 K (0°C) for STP (Standard Temperature and Pressure) or 298.15 K (25°C) for SATP (Standard Ambient Temperature and Pressure). Gas law calculations always use Kelvin — never Celsius or Fahrenheit.
+Why must gas law calculations use Kelvin?
The ideal gas law (PV = nRT) and related gas laws require absolute temperature scales. Using Celsius would give a temperature of 0°C at the freezing point of water, which would falsely suggest zero volume or pressure — physically nonsensical. With Kelvin, doubling the temperature (in K) actually doubles the pressure or volume, which is what the physics requires. Example: doubling from 300 K to 600 K doubles gas pressure, while 'doubling' from 25°C to 50°C (75°C actual K increase) does not.
+What are some important temperatures in Kelvin?
Absolute zero: 0 K (−273.15°C). Liquid helium boiling point: 4.22 K (−268.93°C). Liquid nitrogen boiling point: 77.36 K (−195.79°C). Dry ice (CO₂ sublimation): 194.65 K (−78.5°C). Water freezing: 273.15 K (0°C). Room temperature: 293–298 K (20–25°C). Human body: 310.15 K (37°C). Water boiling: 373.15 K (100°C). Sun surface: 5,778 K. Sun core: ~15,000,000 K.
+What is the difference between Kelvin and Celsius scale?
The Celsius and Kelvin scales have identical degree sizes — 1°C change equals 1 K change. They differ only in their zero points: Celsius starts at the freezing point of water (273.15 K); Kelvin starts at absolute zero. Converting is always simple addition/subtraction: K = °C + 273.15 and °C = K − 273.15. There is no multiplication factor.