Celsius to Kelvin
Convert Celsius to Kelvin for scientific and engineering work. Enter any °C value — get exact Kelvin with thermodynamics context and common scientific reference points.
Enter your values above to see the results.
Tips & Notes
- ✓Kelvin has no degree symbol — write "300 K" not "300°K". The SI standard specifies the unit as kelvin (lowercase k) with symbol K (uppercase). Writing °K is technically incorrect.
- ✓Kelvin is required in all thermodynamic equations: ideal gas law PV = nRT uses T in Kelvin; Wien displacement law λ_max = b/T uses T in Kelvin; Stefan-Boltzmann law P = σT⁴ uses T in Kelvin. Never substitute Celsius in these formulas.
- ✓Absolute zero is 0 K = −273.15°C — the temperature at which molecular motion theoretically ceases. It has never been achieved in practice; the closest approach is within 38 picokelvins of absolute zero in laboratory settings.
- ✓Room temperature in scientific work is typically defined as 25°C = 298.15 K (often approximated as 298 K). Standard temperature and pressure (STP) uses 0°C = 273.15 K. Standard ambient temperature and pressure (SATP) uses 25°C = 298.15 K.
- ✓The Celsius and Kelvin scales have identical degree size — a 1°C change equals a 1 K change. Only the zero point differs. This means temperature differences are the same in both scales: ΔT = 10°C = ΔT = 10 K.
Common Mistakes
- ✗Using 273 instead of 273.15 — for most engineering calculations, 273 K is acceptable. For precision chemistry, thermodynamics, and spectroscopy, the 0.15 difference matters. Use 273.15 unless explicitly told to approximate.
- ✗Writing the degree symbol with Kelvin — Kelvin temperatures are written as "300 K" not "300°K". The kelvin is an absolute unit, not a degree measure. Only Celsius and Fahrenheit use the degree symbol.
- ✗Using Celsius directly in thermodynamic equations — the ideal gas law PV = nRT and other thermodynamic equations require absolute temperature in Kelvin. Substituting Celsius values gives completely wrong results unless ΔT is being calculated.
- ✗Confusing temperature differences vs. absolute temperatures — a temperature change of 10°C equals 10 K (same degree size). But the absolute temperature 10°C = 283.15 K, not 10 K. Only differences are equal; absolute values are not.
- ✗Assuming 0 K = 0°C — absolute zero is 0 K = −273.15°C. The 273.15 K offset is always present when converting absolute values, regardless of the direction of conversion.
Celsius to Kelvin Overview
Kelvin is the temperature scale of science — built on an absolute zero reference point that makes it essential for every equation involving heat, energy, and molecular motion. Unlike Celsius and Fahrenheit, which reflect historical choices of reference points, Kelvin is anchored to a physical absolute.
Celsius to Kelvin formula:
K = °C + 273.15 | Degree size is identical — only the zero point differs
EX: Room temperature 25°C → K = 25 + 273.15 = 298.15 K. Liquid nitrogen −196°C → K = −196 + 273.15 = 77.15 K. Sun surface 5,505°C → K = 5,505 + 273.15 = 5,778.15 KWhy Kelvin — ideal gas law example:
PV = nRT requires T in Kelvin | A gas at 200°C has 473/373 = 1.268× the pressure of the same gas at 100°C (not 2× as Celsius ratio suggests)
EX: Gas at 100°C = 373.15 K. Heated to 200°C = 473.15 K. Pressure ratio = 473.15/373.15 = 1.268 (26.8% increase). Using Celsius directly: 200/100 = 2 — gives a 100% increase, which is completely wrong.Celsius to Kelvin — scientific reference temperatures:
| Celsius (°C) | Kelvin (K) | Scientific Context |
|---|---|---|
| −273.15°C | 0 K | Absolute zero — minimum possible temperature |
| −268.93°C | 4.22 K | Liquid helium boiling point |
| −195.79°C | 77.36 K | Liquid nitrogen boiling point |
| −78.5°C | 194.65 K | Dry ice (CO₂) sublimation point |
| 0.01°C | 273.16 K | Water triple point (Kelvin reference) |
| 25°C | 298.15 K | Standard ambient temperature (SATP) |
| 100°C | 373.15 K | Water boiling point (sea level) |
| 1,538°C | 1,811 K | Iron melting point |
| Scale | Absolute Zero | Water Freezes | Water Boils | Scientific Use |
|---|---|---|---|---|
| Kelvin (K) | 0 K | 273.15 K | 373.15 K | All thermodynamics, astrophysics |
| Celsius (°C) | −273.15°C | 0°C | 100°C | General science, medicine, weather |
| Fahrenheit (°F) | −459.67°F | 32°F | 212°F | US everyday use |
| Rankine (°R) | 0°R | 491.67°R | 671.67°R | US engineering thermodynamics |
Frequently Asked Questions
K = °C + 273.15. Simply add 273.15 to the Celsius temperature. Examples: room temperature 25°C = 298.15 K. Water boiling 100°C = 373.15 K. Dry ice −78.5°C = 194.65 K. Liquid nitrogen −196°C = 77.15 K. Absolute zero −273.15°C = 0 K (the minimum possible temperature). The conversion is linear with no multiplicative factor — just a fixed offset of 273.15.
Kelvin is an absolute temperature scale — 0 K is absolute zero, the minimum possible temperature where molecular kinetic energy theoretically reaches its minimum. Celsius zero (0°C) is an arbitrary reference point (water freezing). Using an absolute scale is essential in thermodynamic equations: the ideal gas law PV = nRT requires T in Kelvin because gas pressure and volume are proportional to absolute temperature, not to Celsius temperature. A gas at 100°C does not have twice the thermal energy of a gas at 50°C (373 K vs 323 K — a ratio of 1.155, not 2).
Absolute zero (0 K = −273.15°C = −459.67°F) is the theoretical temperature at which all thermal motion of atoms and molecules ceases — the minimum possible temperature in the universe. It cannot be achieved in practice due to the Third Law of Thermodynamics, which states that infinite energy would be required to remove the last quantum of thermal energy. Scientists have cooled matter to within billionths of a kelvin of absolute zero using laser cooling and magnetic evaporative cooling. The cosmic microwave background radiation fills the universe at 2.725 K — the "floor" of cosmic temperature.
Multiple standard conditions exist: STP (Standard Temperature and Pressure, IUPAC): 0°C = 273.15 K and 100 kPa — used for gas volume calculations and density. SATP (Standard Ambient Temperature and Pressure): 25°C = 298.15 K and 100 kPa — used for thermodynamic data tables (ΔH°, ΔG°, S°). Standard state conditions: 25°C = 298.15 K at 1 bar pressure — used for standard electrode potentials and equilibrium constants. NTP (Normal Temperature and Pressure, older): 20°C = 293.15 K and 1 atm. Always check which standard is specified in the problem or reference.
Kelvin is the universal temperature unit in astrophysics. The Sun surface: 5,778 K (5,505°C). Solar core: ~15,000,000 K. Hottest known star (WR 102): ~210,000 K. Typical planetary nebula: 7,000-20,000 K. Cosmic microwave background (remnant of Big Bang): 2.725 K. Liquid helium (used in telescope detectors): 4.2 K. Near absolute zero (quantum computing experiments): < 0.001 K. The Kelvin scale spans from essentially 0 K to tens of millions of Kelvin, making it the natural unit for describing the enormous temperature range in the universe.
Key Kelvin values for thermodynamics and chemistry: absolute zero 0 K (−273.15°C); liquid helium boiling 4.22 K (−268.93°C); liquid nitrogen boiling 77.36 K (−195.79°C); dry ice sublimation 194.65 K (−78.5°C); water triple point 273.16 K (0.01°C — the reference calibration point for Kelvin); room temperature 298.15 K (25°C); human body 310.15 K (37°C); water boiling 373.15 K (100°C); iron melting 1,811 K (1,538°C); tungsten melting 3,695 K (3,422°C — highest melting point of any metal).