glunty Temperature converter (C, F, K)
Type a value in Celsius, Fahrenheit, or Kelvin. The other two update live. Local only.
- Runs in your browser
- No sign-up
- No watermark
- No installs
What this tool does
Converts a temperature between the three scales people actually use: Celsius,
Fahrenheit, and Kelvin. It is two-way and live, so typing a valid number in any
field updates the other two instantly, with no button to press and no direction to
choose. The math is the standard set of formulas: F = C * 9/5 + 32,
K = C + 273.15, and their inverses. Everything runs in your browser with
plain JavaScript; nothing you type leaves your machine. Verify it yourself: open
DevTools, open the Network tab, and watch it stay empty. Zero requests.
How to use it
Put your number in the field for the scale you already have. To convert Celsius to
Fahrenheit, type into the Celsius box and read the Fahrenheit box. To go the other
way, type into Fahrenheit. Kelvin works the same. Results round to at most two
decimals with trailing zeros trimmed, so 212.00 shows as
212. Non-numeric input shows a short inline message and leaves the other
fields untouched, and clearing a field empties the others so no stale value lingers.
Two quick sanity checks: -40 reads the same in Celsius and Fahrenheit,
and 0 Kelvin reads -273.15 Celsius (absolute zero). Press
Clear to reset every field.
Common use cases
- Adapting a recipe or oven setting written in the scale you do not use.
- Reading a foreign weather forecast in the units you think in.
- Converting lab or science values to and from Kelvin for physics and chemistry.
- Checking a body temperature quoted in the other scale (37 C is 98.6 F).
- Sanity-checking a sensor reading against absolute zero (-273.15 C).
Common pitfalls
- Kelvin has no degree sign and, in practice, no negatives. You write 300 K, not 300 degrees K. Because Kelvin starts at absolute zero, real physical temperatures are never below 0 K. This tool is pure arithmetic, so it will happily compute a value below absolute zero if you type one, but such a result is not a temperature that can exist.
- Do not add 273 as a shortcut. The Celsius-to-Kelvin offset is 273.15, not 273. Rounding the constant off shifts every answer by 0.15 degrees, which is enough to matter in a lab.
- The two scales cross only at -40. -40 C and -40 F are the same temperature. Away from that point the gap grows, because a Fahrenheit degree is smaller than a Celsius degree (1 C of change equals 1.8 F of change).
- Rounding is for display only. Output is trimmed to two decimals, so a value like 98.6 is shown cleanly rather than as a long floating-point tail. For most everyday needs that is exactly what you want, but do not treat the shown digits as unlimited precision.
Frequently asked questions
- How do I convert Celsius to Fahrenheit?
- Type your value into the Celsius field and read the Fahrenheit field. The formula is F = C * 9/5 + 32, so 20 C is 68 F and 100 C is 212 F. It works both ways: type into Fahrenheit and the Celsius field updates using C = (F - 32) * 5/9. Every field stays in sync as you type, so you never have to pick a direction.
- How does the Kelvin conversion work?
- Kelvin uses the same size degree as Celsius but starts at absolute zero, so K = C + 273.15 and C = K - 273.15. For example, 0 C (the freezing point of water at sea level) is 273.15 K, and 100 C (the boiling point at sea level) is 373.15 K. Kelvin has no negative values in normal use because absolute zero is the coldest temperature that can exist.
- What is absolute zero?
- Absolute zero is the lowest temperature physically possible: -273.15 C, -459.67 F, or exactly 0 K. It is the point at which a system reaches its minimum thermal energy. You can check it in this tool by typing 0 into the Kelvin field and reading -273.15 in the Celsius field.
- At what temperature do Celsius and Fahrenheit read the same?
- At minus 40 degrees. -40 C equals -40 F, which is the single point where the two scales meet. You can confirm it by typing -40 into either the Celsius or the Fahrenheit field. This happens because the two scales have different zero points and different degree sizes, and their lines cross at exactly -40.
- How does this converter round results?
- Results are rounded to at most two decimal places, and trailing zeros are trimmed, so 212.00 shows as 212 and 273.15 stays 273.15. Two decimals is plenty for cooking, weather, and most lab work. The underlying formulas are simple, so if you ever need extra precision for one value you can compute it by hand.
- Does the converter send my numbers anywhere?
- No. Every conversion runs in your browser using plain JavaScript arithmetic. Nothing you type is uploaded, logged, or sent to a server. You can verify it: open DevTools, watch the Network tab, and it stays empty while you use the tool. Zero requests.
Cite this tool
For academic, journalistic, or technical references. Pick a format:
Citations use 2026 as the publication year. Access date is left as a fillable placeholder where the citation style expects one.