Temperature Converter

How this is calculated

TEMPERATURE IS NOT LIKE LENGTH OR WEIGHT. Every other converter on this site multiplies by a factor, because zero means the same thing in both units - zero metres is zero feet. Temperature scales have different zero points, so each conversion is a multiplication AND a shift, and you cannot convert a temperature by scaling it. This is why doubling 10°C does not give you double the heat, and why a temperature DIFFERENCE converts differently from a temperature (see below). THE CONVERSIONS ARE EXACT BY DEFINITION. Since 1954 the Celsius scale has been defined against the kelvin, with 0°C at exactly 273.15 K, and the Fahrenheit degree is exactly five ninths of a Celsius degree with its zero offset by 32. So C = (F − 32) × 5/9 and K = C + 273.15 are definitions, not approximations. ⚠️ A DIFFERENCE IS NOT A TEMPERATURE. "It rose by 10°C" converts to a rise of 18°F, not to 50°F. When you are converting a CHANGE or a RANGE, use only the ratio 9/5 and drop the 32 entirely. This tool converts temperatures, so if you feed it a difference the answer will be wrong by the offset. It is one of the most common conversion errors in recipes, weather reports and datasheets. OVEN GAS MARK IS A REAL SCALE, AND IT ONLY EXISTS OVER A REAL RANGE. Gas mark 1 is 275°F and each further mark adds 25°F, so mark 4 is 350°F and mark 9 is 475°F. The tool leaves the gas mark BLANK outside that range, in both directions, rather than extending a straight line into territory where there is nothing to extend it to. Below mark 1 the scale switches to fractions — mark ½ is 250°F and mark ¼ is 225°F — which do not follow the same 25-degree spacing, so the linear rule genuinely does not hold there. The fractional marks are on the printable sheet. Above mark 10 (500°F) the arithmetic still works but there is no such position on any domestic oven, and a "gas mark 32" is a number with nothing behind it. Blank is the honest answer at both ends. ⚠️ PUBLISHED OVEN TABLES ARE ROUNDED, AND THIS TOOL IS NOT. A recipe book says 350°F is 180°C; the exact conversion is 176.7°C. Cookbooks round to the numbers an oven dial actually has, which is sensible for cooking and wrong as arithmetic. If your converted figure looks slightly off against a recipe table, this is almost always why — and for an oven, the rounded number is the one to use. BELOW ABSOLUTE ZERO NOTHING IS GUARDED, DELIBERATELY. Absolute zero is −273.15°C, −459.67°F, or 0 K. If you enter something colder the Kelvin figure goes NEGATIVE, which is the clearest possible signal that the temperature you typed cannot exist. Showing a row of dashes instead would hide why. FAN AND CONVECTION OVENS RUN COOLER THAN THE DIAL, and this tool does not adjust for that, because the offset depends on the oven. Your manufacturer's manual is the authority; a generic figure is a guess dressed up as a conversion.

Common questions

Why can't I just multiply to convert a temperature?

Because the scales have different zero points. Every other unit converter works by scaling - zero metres is zero feet, so one factor does the whole job. Zero degrees Celsius is 32 degrees Fahrenheit, so a conversion needs a multiplication AND a shift. That is also why doubling the number does not double anything physical: 20°C is not twice as hot as 10°C in any meaningful sense, though 20 K genuinely is twice 10 K, because the Kelvin scale starts at absolute zero.

How do I convert a temperature DIFFERENCE?

Use the ratio only and drop the offset entirely. A rise of 10°C is a rise of 18°F, because 10 × 9/5 = 18. It is not 50°F - that would be converting 10°C as a temperature rather than as a change. The same applies to a range, a tolerance or a margin: '±5°C' is '±9°F'. This is one of the most common conversion errors in recipes, weather reporting and technical datasheets, and it is invisible because both answers look reasonable.

Why is the gas mark sometimes blank?

Because the scale only exists over a real range, and outside it this tool will not guess. From mark 1 upward it is regular - mark 1 is 275°F and every further mark adds 25°F, so mark 4 is 350°F and mark 9 is 475°F. Below mark 1 it switches to fractions: mark ½ is 250°F and mark ¼ is 225°F, which do not follow the same 25-degree spacing, so the linear rule genuinely fails there. Above mark 10 (500°F) the arithmetic still works but no domestic oven has such a position, so a figure like 'gas mark 32' would be a number with nothing behind it. The field is left blank at both ends, and the fractional marks are on the printable sheet.

Why doesn't this match my recipe book's oven table?

Because cookbook tables are rounded to the numbers an oven dial actually has, and this tool is not rounded. A book says 350°F is 180°C; the exact conversion is 176.7°C. Both are 'right' for their purpose - the rounded figure is the one to set your oven to, and the exact one is the arithmetic. If a converted number looks slightly off against a table, this is nearly always the reason rather than an error in either.

What is absolute zero?

The lowest temperature that can exist: −273.15°C, −459.67°F, or 0 K. It is the point at which a system has the minimum energy it can have. This tool does not block colder inputs - if you enter one, the Kelvin figure comes out NEGATIVE, which tells you immediately that the temperature you typed is impossible. Blanking every field instead would hide the reason, and a negative Kelvin is about as clear a signal as a number can give.

What about fan or convection ovens?

They run cooler than a conventional oven at the same dial setting, but by how much depends on the oven, so this tool does not adjust for it. Your manufacturer's manual is the authority and will state the offset for your model. A single generic figure applied to every oven is a guess presented as a conversion, which is exactly the kind of number this site tries not to publish.

What about Rankine?

Not offered, deliberately. Rankine is an absolute scale like Kelvin but using Fahrenheit-sized degrees, so absolute zero is 0°R and water freezes at 491.67°R. It appears in some American engineering work and essentially nowhere else. Adding a fourth scale that almost no reader wants would make the three that matter harder to read, which is the same reason nautical miles are left out of the length converter.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Temperature Converter at https://www.bfcbrilliance.com/tools/temperature-converter.

What I entered:
- Temperature: ___
- Measured in: ___

What it calculated:
- Celsius: ___
- Fahrenheit: ___
- Kelvin: ___
- Oven gas mark: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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