Temperature Conversion Reference

The conversions (exact by definition)

Fahrenheit to Celsius

(F − 32) × 5/9

Celsius to Fahrenheit

(C × 9/5) + 32

Celsius to Kelvin

C + 273.15

Kelvin to Celsius

K − 273.15

⚠ A DIFFERENCE

× 9/5 only — never add the 32

The scales cross at

−40° — the same in C and F

Oven chart — gas mark, °F, °C (as printed in books)

Gas mark ¼

225°F / 110°C

Gas mark ½

250°F / 130°C

Gas mark 1

275°F / 140°C

Gas mark 2

300°F / 150°C

Gas mark 3

325°F / 170°C

Gas mark 4

350°F / 180°C

Gas mark 5

375°F / 190°C

Gas mark 6

400°F / 200°C

Gas mark 7

425°F / 220°C

Gas mark 8

450°F / 230°C

Gas mark 9

475°F / 240°C

⚠ The °C column is ROUNDED

350°F is exactly 176.7°C

⚠ Below mark 1

fractions — NOT 25°F apart

⚠ Above mark 10 (500°F)

no marked position on a home oven

Fixed points worth knowing

Absolute zero

−273.15°C / −459.67°F / 0 K

Water freezes

0°C / 32°F / 273.15 K

Water boils (sea level)

100°C / 212°F / 373.15 K

Body temperature

37°C = 98.6°F exactly

A comfortable room

20°C = 68°F exactly

Fridge (typical)

4°C = 39.2°F

Freezer (typical)

−18°C = −0.4°F

⚠ The freezer pair is a CONVENTION, not an equality

0°F = −17.8°C, near −18°C

Doing it in your head

°C to °F, quick

double it and add 30

°F to °C, quick

subtract 30 and halve

How far off is that?

a few degrees in the everyday range

20°C exact / quick

68°F / 70°F

⚠ For cooking or dosing

use the exact formula

Where temperature mistakes actually bite

• A temperature CHANGE converted with the 32 offset included
• An oven set in °F when the recipe meant °C, or the reverse
• A fan oven run at the conventional temperature
• Gas mark read off a linear rule below mark 1
• A rounded cookbook °C used as an exact figure in arithmetic
• Meat probe target temperatures mixed between scales
• A negative Kelvin figure ignored rather than treated as impossible

−40 is the same in both

Celsius and Fahrenheit cross at −40: −40°C is −40°F. It is the one temperature where the two scales agree, which makes it a fast sanity check — if your conversion formula gives the same answer at −40 in both directions, you have the offset and the ratio the right way round.

A rise of 10°C is a rise of 18°F

Not 50°F. When converting a CHANGE, a RANGE or a TOLERANCE, use the 9/5 ratio and drop the 32 entirely. The offset belongs to the position of the zero point, and a difference has no zero point. This single mistake accounts for a large share of conversion errors in recipes and datasheets, and both answers look plausible enough to survive.