Celsius to Kelvin Converter
Instantly convert degrees Celsius to Kelvin, Fahrenheit, Rankine, and other temperature scales — with live precision control, quick presets for common temperatures, an absolute-zero-aware scale comparison, and a downloadable PDF report.
Temperature is an offset scale: K = °C + 273.15 (exact), °F = °C × 9/5 + 32. Absolute zero is 0 K = −273.15 °C — for reference only.
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Celsius to Kelvin Conversion — Complete Guide for 2026
Converting degrees Celsius (°C) to Kelvin (K) is essential in science, engineering, and anywhere absolute temperature matters — from chemistry homework and gas-law calculations to HVAC specifications and the color temperature printed on light bulbs. Unlike most unit conversions, it isn’t a multiplication: the two scales use the same size of degree but start from different zero points. The key relationship is exact: K = °C + 273.15, so 0 °C = 273.15 K and absolute zero (0 K) = −273.15 °C.
Our free Celsius to Kelvin Converter takes a temperature in degrees Celsius — including negative values down to absolute zero — and returns Kelvin at your chosen precision, along with Fahrenheit and Rankine and four historical scales (Réaumur, Newton, Rømer, and Delisle). Quick presets, a linear scale-comparison chart, a reference table from absolute zero to broiling, and a downloadable PDF report make it useful for a quick check or for lab, class, and project records.
How to Use the Celsius to Kelvin Converter in 4 Steps
A complete °C-to-K conversion takes a few seconds. Enter a temperature or tap a preset, choose your precision, and download a PDF report you can attach to a lab write-up, assignment, or spec sheet.
Enter the Temperature in °C
Type any temperature in degrees Celsius, including negative values — from a winter night to cryogenic lab conditions, down to absolute zero at −273.15 °C. Decimals are supported, and the result updates on every keystroke.
Or Tap a Quick Preset
Reference temperatures are one tap away: −40 °C (where °C and °F meet), 0 °C (freezing), 20 °C (room), 25 °C (standard reference), 37 °C (body), and 100 °C (boiling). The active preset stays highlighted.
Set Decimal Precision
Use the input or slider to pick 0 to 8 decimal places (the default is 2, matching the exact 273.15 offset). More decimals suit laboratory and technical records; everyday temperatures rarely need more than one.
Review & Download PDF
See your temperature in Kelvin, Fahrenheit, Rankine, Celsius, and the historical scales, plus a chart comparing the same temperature across scales. Click Download PDF for a two-page branded report with every conversion, the chart, and a highlighted reference table.
Why K = °C + 273.15
The Celsius scale was built around water: roughly 0 °C where it freezes and 100 °C where it boils at sea level. The Kelvin scale, named after Lord Kelvin, starts instead at absolute zero — the point at which a system has the least possible thermal energy — and uses the same size of degree. Absolute zero sits at exactly −273.15 °C, so every Kelvin value is simply the Celsius value plus 273.15.
The kelvin is the SI base unit of thermodynamic temperature. Since the 2019 redefinition of the SI, it has been defined by fixing the Boltzmann constant at exactly 1.380649 × 10⁻²³ J/K, and the degree Celsius is defined as the kelvin offset by 273.15. That makes the conversion exact by definition — there is no rounding in the offset. Kelvin is written without a degree sign: 300 K, read “300 kelvins.”
Temperatures vs temperature differences
Because Celsius and Kelvin are offset scales, it matters whether you’re converting a reading or a difference:
- A temperature reading — add 273.15. A room at 22 °C is 295.15 K.
- A temperature difference — no offset. A 10 °C rise is a 10 K rise (and an 18 °F rise).
- Ratios and gas laws — always use Kelvin. Warming air from 20 °C to 40 °C doesn’t double its absolute temperature; it goes from 293.15 K to 313.15 K, an increase of only about 6.8%.
That last point is why physics and chemistry formulas — the ideal gas law, radiation, and thermodynamic efficiency — require absolute temperature. Because the conversion itself is exact, the only real uncertainty is in the thermometer or sensor reading you start with.
What the Celsius to Kelvin Converter Calculates
More than a single Kelvin figure — the tool shows your temperature on every major scale, plus four historical ones, formatted for class, lab, engineering, or reference use.
Kelvin (Hero Result)
The headline result adds exactly 273.15 to your Celsius value and shows it at the precision you select, with a summary line beneath it that also gives Fahrenheit and Rankine.
Fahrenheit
Fahrenheit (°C × 9/5 + 32) is the everyday scale in the US — thermostats, weather, ovens, and cooking. Having it beside Kelvin lets you connect a scientific value to a familiar one.
Rankine
Rankine ((°C + 273.15) × 9/5) is the absolute scale with Fahrenheit-sized degrees. Like Kelvin, it starts at absolute zero and appears in some US engineering and thermodynamics work.
Historical Scales
Réaumur (°C × 4/5), Newton (°C × 33/100), Rømer (°C × 21/40 + 7.5), and Delisle ((100 − °C) × 3/2) are 18th-century scales shown for history, old texts, and classroom curiosity.
Linear Scale Comparison
Unlike the log charts on ratio converters, this chart uses a linear axis, because temperatures can be negative. It shows the same temperature on the Celsius, Kelvin, Fahrenheit, and Rankine scales side by side.
Reference Table & PDF
A reference table of landmark temperatures — from absolute zero through freezing, room, body, boiling, and oven temperatures — highlights your input when it matches, and the two-page PDF bundles everything for sharing or record-keeping.
Celsius to Kelvin Conversion Chart — Common Temperatures
Bookmark this page or screenshot the table below for instant reference. Every value uses the exact relations K = °C + 273.15, °F = °C × 9/5 + 32, and °R = K × 1.8. Household examples are typical settings and vary by appliance, altitude, and person.
| Celsius | Kelvin | Fahrenheit | Rankine | Common Reference |
|---|---|---|---|---|
| −273.15 °C | 0.00 K | −459.67 °F | 0.00 °R | Absolute zero |
| −40 °C | 233.15 K | −40.00 °F | 419.67 °R | Where °C and °F are equal |
| −18 °C | 255.15 K | −0.40 °F | 459.27 °R | Home freezer (about 0 °F) |
| 0 °C | 273.15 K | 32.00 °F | 491.67 °R | Water freezes |
| 4 °C | 277.15 K | 39.20 °F | 498.87 °R | Refrigerator (typical) |
| 20 °C | 293.15 K | 68.00 °F | 527.67 °R | Room temperature |
| 25 °C | 298.15 K | 77.00 °F | 536.67 °R | Standard lab reference |
| 37 °C | 310.15 K | 98.60 °F | 558.27 °R | Average body temperature |
| 60 °C | 333.15 K | 140.00 °F | 599.67 °R | Hot water heater, high setting |
| 100 °C | 373.15 K | 212.00 °F | 671.67 °R | Water boils (sea level) |
| 180 °C | 453.15 K | 356.00 °F | 815.67 °R | Moderate oven (baking) |
| 200 °C | 473.15 K | 392.00 °F | 851.67 °R | Hot oven (roasting) |
| 260 °C | 533.15 K | 500.00 °F | 959.67 °R | Very hot oven / broiling |
How to Use Celsius and Kelvin in Practice
The most common reasons people convert Celsius to Kelvin are science and engineering calculations, HVAC and equipment specifications that quote temperature differences in kelvins, and the Kelvin color-temperature ratings on light bulbs. Each one uses Kelvin a little differently, so it helps to know which kind of number you’re looking at.
The manual calculation
Step 1: If you have a temperature reading, add 273.15. Step 2: If you have a temperature difference, keep the same number — just change the unit. Step 3: For Fahrenheit differences, multiply by 1.8. For a room at 22 °C cooled by an air conditioner supplying 13 °C air against 24 °C return air:
Temperature difference: 24 °C − 13 °C = 11 °C = 11 K
Same difference in Fahrenheit: 11 × 1.8 = 19.8 °F
Result: 295.15 K room; 11 K (19.8 °F) supply-to-return split
Enter a reading into the calculator to get Kelvin, Fahrenheit, and Rankine at once. For differences, remember the rule: a change of 1 °C is a change of 1 K — adding 273.15 to an 11-degree split would wrongly turn it into 284.15 K.
Kelvin on light bulbs
Bulb packaging lists color temperature in Kelvin. It describes the color of the light, not how hot the bulb runs:
- 2700 K — warm white, similar to traditional incandescent bulbs; common in living rooms and bedrooms.
- 3000 K — soft white, slightly crisper; popular in kitchens and bathrooms.
- 4000 K — neutral or cool white; often used in garages, workspaces, and offices.
- 5000–6500 K — daylight; bright and bluish, used for task lighting and some commercial spaces.
Celsius to Kelvin — Key Conversion Numbers
The Celsius to Kelvin Converter Is Built For You If…
Whether you’re solving a gas-law problem, reading an HVAC spec, or choosing light bulbs — this calculator gives you the exact answer in seconds, with a report you can save and share.
Students & Teachers
Chemistry & physicsGas laws, thermodynamics, and radiation formulas all require absolute temperature. Converting correctly — and knowing when not to add 273.15 — is one of the most common sources of lost marks in science classes.
- Always use Kelvin in PV = nRT and similar formulas
- Add 273.15 to readings, not to differences
- Write K without a degree sign
- Check that no answer comes out below 0 K
Engineers & HVAC Technicians
Specs & temperature splitsEquipment data sheets, especially from international manufacturers, often give temperatures in °C and temperature differences in K. Converting cleanly between °C, K, °F, and °R keeps load calculations and commissioning reports consistent.
- A spec of “ΔT = 5 K” means a 5 °C (9 °F) difference
- °R = K × 1.8 for US thermodynamic tables
- Label readings and differences clearly
- Attach the PDF to test and commissioning records
Homeowners & DIYers
Lighting, comfort & appliancesKelvin shows up at home on light-bulb boxes, smart-lighting apps, and some thermostat and appliance specs. Understanding what the number means helps you choose the right bulbs and read equipment manuals written for international markets.
- 2700–3000 K for warm, cozy rooms
- 4000 K+ for garages, workshops, and task areas
- Keep one color temperature per room for a consistent look
- Bulb Kelvin is light color, not heat
7 Tips for Accurate Celsius to Kelvin Conversions
The conversion is exact, but temperature is easy to mishandle. Most mistakes come from multiplying instead of adding, offsetting differences, forgetting absolute zero, and misreading color temperature. These rules keep every conversion trustworthy.
Add, Don’t Multiply
Celsius to Kelvin is an offset, not a ratio: add 273.15. Doubling a Celsius temperature does not double the Kelvin temperature, and there’s no single multiplier that converts between them.
Don’t Offset Differences
A temperature change is the same number in °C and K. A 15 °C rise is a 15 K rise — adding 273.15 to it is a common error in homework and HVAC calculations.
Nothing Goes Below 0 K
Absolute zero (0 K = −273.15 °C) is the lowest possible temperature. If you get a negative Kelvin value, check for a typo or a misplaced minus sign in the Celsius reading.
Write Kelvin Correctly
Write 300 K, not 300 °K, and say “kelvins,” not “degrees Kelvin.” Celsius and Fahrenheit keep the degree sign; Kelvin doesn’t.
Use Kelvin for Ratios and Gas Laws
Any formula that multiplies or divides temperature — gas laws, efficiency, radiation — needs an absolute scale. Using Celsius there gives wrong answers, and dividing by 0 °C is impossible.
Boiling Point Depends on Altitude
Water boils at about 100 °C (373.15 K) only at sea-level pressure. At higher elevations it boils at a lower temperature, which matters for cooking, canning, and lab work.
Memorize Three Anchors for Mental Math
0 °C = 273.15 K. 100 °C = 373.15 K. 0 K = −273.15 °C. With these you can check any answer in your head — room temperature is about 293 K, and body temperature is about 310 K.
Celsius to Kelvin Converter — Frequently Asked Questions
Everything you need to know about converting Celsius to Kelvin, why the offset is 273.15, how temperature differences work, and what Kelvin means on light bulbs.
Add 273.15 to the Celsius temperature: K = °C + 273.15. For example, 25 °C + 273.15 = 298.15 K. The conversion is an addition, not a multiplication, because the two scales use the same size of degree but start from different zero points.
Subtract 273.15 from the Kelvin temperature: °C = K − 273.15. For example, 300 K − 273.15 = 26.85 °C. Common values: 0 °C = 273.15 K, 100 °C = 373.15 K, and −40 °C = 233.15 K. This converter takes Celsius as its input; to check a result, enter the Celsius figure you calculated and confirm the Kelvin result matches.
Kelvin starts at absolute zero, the lowest possible temperature, while Celsius starts near the freezing point of water. Absolute zero is exactly −273.15 °C, and a one-degree step is the same size on both scales, so the offset between them is exactly 273.15. Since 2019, the kelvin has been defined by fixing the Boltzmann constant at 1.380649 × 10⁻²³ J/K, and the degree Celsius is defined as the kelvin minus 273.15.
The kelvin is the SI base unit of thermodynamic temperature, so it is written like other units: 300 K, read as 300 kelvins, not 300 degrees Kelvin. The degree sign and the phrase degrees Kelvin were dropped by international agreement in 1967. Celsius and Fahrenheit still use the degree symbol.
No. Zero kelvin is absolute zero, the lowest temperature physically possible, so Kelvin values are never negative. That means the lowest valid Celsius input is −273.15 °C, which equals 0 K. If a calculation gives a negative Kelvin value, check for a typo or a missing minus sign in the Celsius figure.
Yes. The Celsius degree and the kelvin are the same size, so temperature differences are identical on both scales. A rise of 5 °C is a rise of 5 K. Do not add 273.15 to a temperature difference — only to an actual temperature reading. A difference of 1 K or 1 °C equals 1.8 °F.
On light bulbs, Kelvin describes color temperature — how warm or cool the light looks — not how hot the bulb gets. Around 2700 K is warm white, 3000 K is soft white, about 4000 K is neutral or cool white, and 5000 K to 6500 K looks like daylight. Converting these values to Celsius is not useful for choosing bulbs; compare them directly in Kelvin.
To convert Celsius to Fahrenheit, multiply by 9/5 and add 32: °F = °C × 9/5 + 32. From Kelvin, first subtract 273.15, then apply the same formula. For example, 25 °C = 77 °F, 37 °C = 98.6 °F, and 298.15 K = 77 °F. At −40, the Celsius and Fahrenheit scales read the same number.
Rankine is an absolute temperature scale that uses Fahrenheit-sized degrees. Like Kelvin, it starts at absolute zero (0 °R). To convert, °R = °F + 459.67, or °R = K × 1.8. For example, 25 °C = 298.15 K = 536.67 °R. Rankine appears in some US engineering and thermodynamics calculations.
Room temperature of 20 °C is 293.15 K, and the common laboratory reference temperature of 25 °C is 298.15 K. An average body temperature of 37 °C is 310.15 K. Water freezes at 273.15 K and boils at about 373.15 K at sea level.
They are historical temperature scales from the 1700s that are rarely used today. Réaumur = °C × 4/5, Newton = °C × 33/100, Rømer = °C × 21/40 + 7.5, and Delisle = (100 − °C) × 3/2. The Delisle scale runs backwards, so higher temperatures have lower Delisle numbers. The converter shows them for historical and educational interest.
The converter uses exact definitions: K = °C + 273.15, °F = °C × 9/5 + 32, and °R = (°C + 273.15) × 9/5, along with the standard formulas for the historical scales. Calculations use double-precision floating-point arithmetic, and display precision is adjustable from 0 to 8 decimal places. In practice, accuracy is limited by the thermometer or sensor that produced the reading, not by the conversion.
Accuracy note: The HomeExpertly Celsius to Kelvin Converter uses the exact relations K = °C + 273.15, °F = °C × 9/5 + 32, and °R = (°C + 273.15) × 9/5, consistent with the International System of Units (SI) as maintained by the International Bureau of Weights and Measures (BIPM) and recognized by the U.S. National Institute of Standards and Technology (NIST). Historical scales (Réaumur, Newton, Rømer, Delisle) use their standard modern conversion formulas. All calculations are mathematically precise to the decimal precision you select (up to 8 places). However, results are for informational and reference purposes only. Temperatures below absolute zero (−273.15 °C) are not physically possible. Household temperatures, appliance settings, boiling points, and light-bulb color temperatures on this page are typical figures that vary by product, altitude, and conditions. This converter is not a medical tool — body-temperature figures are general averages, and health concerns should be discussed with a healthcare provider. For laboratory, industrial, food-safety, or engineering applications where temperature is critical, always verify readings independently using calibrated instruments and the applicable standards and procedures. HomeExpertly is not responsible for any consequences arising from the use of these conversions.