The formula
How to calculate temperature chart
This page is built around the reference table below — the Celsius, Fahrenheit and Kelvin values people look up most often, from well below freezing to boiling point — plus the calculator above for any value not already in the table.
The table steps through round numbers and a few named reference points (freezing, body temperature, boiling) rather than every integer, since those are the values that actually get looked up — a weather forecast, an oven temperature, a fever reading.
What to enter:
- Temperature (°C)
No submit button: type and the answer moves. Your inputs end up in the link, so the page can be shared already filled in.
Where more decimal places matter than the fields above display, the underlying calculation is not rounded until the final figure is shown — the precision used internally is higher than what is printed, which matters for anyone chaining this result into a further calculation of their own.
Why temperature chart matters
The formula behind temperature chart is standard and appears in the same form across textbooks and reference material; what a calculator adds is speed and the ability to see instantly how the result responds to a change in any one of the inputs, which is far slower to do by hand.
Beyond a single check, the same calculation is worth rerunning whenever a measured input changes — a new reading, a corrected value, an updated assumption — since the result here always reflects exactly what is currently in the fields above rather than a value calculated once and then left stale.
A formula like this one is rarely the last step in a piece of work — the figure it produces usually feeds into a further calculation, a comparison against a published value, or a write-up that needs to state both the result and how confident it is. Getting this step right the first time, rather than propagating a small arithmetic slip through several more steps, is the main practical reason to check a manual calculation against a tool like this one before building on top of it.
In practice, a formula like this one is most often reached for at the exact moment a manual calculation needs checking against a deadline — a lab report due, a problem set to submit — which is precisely the situation where a small arithmetic slip is easiest to miss and most costly to leave uncorrected. Running the same inputs through an independent calculator catches that class of error reliably.
Worked example
Work through the defaults on this page:
- Temperature: 20 °C
That gives:
- Fahrenheit: 68 °F
- Kelvin: 293.15 K
The figures above are the calculator's own default values, shown purely so the working is visible rather than hidden — the same steps apply exactly to your own numbers, entered in the fields at the top of this page.
Reading the result
Reading the table: each row is one true temperature expressed in three scales at once, so 20 °C, 68 °F and 293.15 K are the same temperature, not three different ones. Pick whichever scale the number you already have is in, and read across.
Where this goes wrong. Oven temperatures are a common source of confusion because recipe conventions differ by country: a US recipe in Fahrenheit and a European one in Celsius are not simply rounded versions of each other — 350 °F is 177 °C, not 175 °C, though the rounding rarely matters for baking.
A result that is wrong by an exact factor of ten, a hundred or a similar round number is almost always a units error rather than a mistake in the formula itself — checking each input against the unit stated beside it is the fastest way to track it down.
Conventions vary by region and what people are used to, but a widely used rough guide is: below 10 °C (50 °F) cold, 10–20 °C (50–68 °F) cool, 20–27 °C (68–80 °F) warm, above 27 °C (80 °F) hot.
Kelvin is included for completeness and because it is the scale used in science and by some weather instruments internally — the same 20 °C reading a forecast reports is 293.15 K to a physicist, and having all three side by side makes the relationship concrete.
It returns fahrenheit. With 20 °C temperature, that comes to 68 °F. Change any field and the figure moves with it.
Generally, no more than the least precise input justifies — a result reported to six decimal places from inputs measured to two significant figures is implying a precision the calculation does not actually have. The calculator shows full precision so you can round appropriately for your own use.
Yes — the equation shown in the formula section above is the standard form used in textbooks and reference material for this calculation, not a simplified or approximate version.
Yes, in the sense that it applies the correct standard formula and returns an accurate result for the inputs given — but check your own course or publication's requirements for how results should be rounded, presented and referenced, since those conventions vary and are not something a calculator can know on your behalf.
Celsius, Fahrenheit and Kelvin reference table
| Celsius | Fahrenheit | Kelvin | Reference |
|---|---|---|---|
| −40 °C | −40 °F | 233.15 K | Celsius and Fahrenheit cross here |
| −20 °C | −4 °F | 253.15 K | Severe cold |
| −10 °C | 14 °F | 263.15 K | Hard frost |
| 0 °C | 32 °F | 273.15 K | Water freezes |
| 10 °C | 50 °F | 283.15 K | Cool |
| 15 °C | 59 °F | 288.15 K | Mild |
| 20 °C | 68 °F | 293.15 K | Room temperature |
| 25 °C | 77 °F | 298.15 K | Warm |
| 30 °C | 86 °F | 303.15 K | Hot |
| 37 °C | 98.6 °F | 310.15 K | Body temperature |
| 40 °C | 104 °F | 313.15 K | Heatwave |
| 100 °C | 212 °F | 373.15 K | Water boils (sea level) |