Aisha K.
Mar 12, 2026
Clean layout and the results update instantly. Exactly what I needed for a quick planning check.
Unit Converters
Celsius to Kelvin Converter (°C to K)
K = °C + 273.15. The size of a kelvin equals a Celsius degree.
Labs and gas laws want kelvin because zero means zero motion, not “really cold in Celsius.” Add 273.15. You never write a degree sign on K. 25 °C room temp is 298.15 K.
Celsius
Going the other way? Open the reverse converter
°C → K
298.15 K
0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
- You typed
- 25 °C
- How it’s calculated
- K = °C + 273.15. The size of a kelvin equals a Celsius degree.
Plain-English guide
Terms & how it works
Confused by a field? Read the short definitions here while you use the tool.
Celsius
The “Celsius” value used in this tool’s formula. Adjust it to see results update live.
How this calculator works
Labs and gas laws want kelvin because zero means zero motion, not “really cold in Celsius.” Add 273.15. You never write a degree sign on K. 25 °C room temp is 298.15 K. K = °C + 273.15. The size of a kelvin equals a Celsius degree. Example: 0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
K = °C + 273.15. The size of a kelvin equals a Celsius degree.
Example: 0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
When to use this Celsius to Kelvin
Common use cases
- Labs and gas laws want kelvin because zero means zero motion, not “really cold in Celsius.” Add 273.15. You never write a degree sign on K. 25 °C room temp is 298.15 K.
- Sanity-check with this case: 0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
- The relationship is: K = °C + 273.15. The size of a kelvin equals a Celsius degree.
Localized examples
- Unit Converters: the example on this page uses the same formula as the widget.
What you get
- Fields: Celsius
- K = °C + 273.15. The size of a kelvin equals a Celsius degree.
- Example on the page: 0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
How to Convert Celsius to Kelvin Step-by-Step
- 1Enter Celsius. Use the values you have, not a catalog average, unless that is all you know.
- 2K = °C + 273.15. The size of a kelvin equals a Celsius degree.
- 3Worked case: 0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
- 4Check which dictionary the other person is using — US or UK, decimal or 1,024 — then trust the number.
Governing formula
K = °C + 273.15. The size of a kelvin equals a Celsius degree.
0 °C → 273.15 K. −273.15 °C → 0 K (absolute zero). 100 °C → 373.15 K.
Example: set Celsius = 25, then read the result.
Variable definitions
- value
Celsius
The “Celsius” field. Default 25; typical range -273.15–5000.
- The conversion (K = °C + 273.15. The size of a kelvin equals a Celsius degree.) does not pick US vs UK gallons, SI vs binary megabytes, or Mach at altitude for you. Read the footnote on the page.
- Nothing here is uploaded for the calculation itself.
Frequently Asked Questions
Ice point is 273.15 K. Dropping the .15 is a lab error.
Related calculators
Unit Converters
- Celsius to RankineWhen a US customaries thermodynamics problem wants an absolute temperature but you measured Celsius: convert to kelvin, then × 9/5. 20 °C is 527.67 °R. Absolute zero is 0 °R on both sides of the ocean.
- Kelvin to CelsiusDatasheets list 298 K and you wanted “was that a warm lab?” Subtract 273.15. 298.15 K is 25 °C. Liquid nitrogen’s 77 K is −196 °C.
- Celsius Heat Units to JoulesA Celsius heat unit is the heat to raise 1 pound of water by 1 °C — about 1,899 J. Old HVAC and process papers use CHU. If you expected BTU, you are on the Fahrenheit twin (1 lb × 1 °F). Do not mix them in a load calc.
- Celsius to FahrenheitWeather apps, ovens, and fever debates. Multiply °C by 9/5 and add 32. Room temperature 20 °C is 68 °F. Body temperature 37 °C is 98.6 °F. The “times two plus 30” trick is only for sidewalks.
- Fahrenheit to CelsiusUS thermostats still speak Fahrenheit. Science and most of the planet speak Celsius. Subtract 32, then multiply by 5/9. 72 °F indoors is 22.2 °C, not “22 unless you like arguing about hoodies.”
- Fahrenheit to KelvinWhen a US weather number has to enter an ideal-gas problem: convert °F to °C in your head, then add 273.15 — or let this page do both. 68 °F is 293.15 K.
Get a note when we add a planner
Occasional email when something new is worth opening. We never share your address. Unsubscribe anytime.
Discover & search
Explore More Tools
Related tools in Unit Converters — strengthening topical internal links.
Same category · 3 tools
Browse all →Meters to Kilometers
Unit Converters
A 5K is 5,000 meters, not 5 kilometers on the nose if your watch is sloppy. Divide meters by 1,000. Track races, building plans, and “how far was that hike” all live in this split.
Feet to Meters
Unit Converters
US height, ceiling height, and lumber still arrive in feet. Meter plans do not. One foot is exactly 0.3048 m — not “about a third.” Use this when a listing says 10 ft ceilings and the architect works in meters.
Inches to Centimeters
Unit Converters
Monitor diagonals, waist measurements, and photo prints still come in inches. Clothing charts in Europe come in cm. Multiply inches by 2.54. That factor is exact, not a kitchen guess.
Community
Reviews & Ratings
See what others think about this tool, then leave your own rating to help improve CalculioHub.
4.8
out of 5.0
4 reviews
Daniel R.
Feb 28, 2026
Very usable on mobile. Would love a save/export option later, but the math feels solid.
Priya S.
Feb 3, 2026
The FAQ section answered my questions before I even had to search. Smooth dark mode too.
Marcus L.
Jan 19, 2026
Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.
Improve this tool
Suggestion Box
Share an idea, report a bug, or send general feedback for Celsius to Kelvin. Your input helps shape what we build next.