Whether you’re traveling abroad, following a recipe from another country, or just trying to understand the weather forecast, temperature conversion is a skill you’ll use more often than you think. The two most common temperature scales — Celsius and Fahrenheit — can feel like different languages, but converting between them is simpler than it seems.

This guide covers everything you need: the exact formulas, mental math shortcuts, common reference points, and practical scenarios where temperature conversion matters.

The Three Temperature Scales

Celsius (°C)

Used by nearly every country in the world, Celsius sets 0° at the freezing point of water and 100° at the boiling point. It’s the standard for science, weather, and daily life in most of the world.

Fahrenheit (°F)

Primarily used in the United States and a few other territories, Fahrenheit sets 32° at the freezing point of water and 212° at the boiling point. The scale was designed so that typical weather temperatures fall roughly between 0° and 100°.

Kelvin (K)

The scientific standard, Kelvin uses the same scale as Celsius but starts at absolute zero (-273.15°C). It’s used in physics and chemistry. Note: Kelvin doesn’t use the degree symbol.

The Exact Conversion Formulas

Celsius ↔ Fahrenheit

°F = °C × 9/5 + 32

°C = (°F - 32) × 5/9

The fraction 9/5 is the same as 1.8, so you can also write:

°F = °C × 1.8 + 32
°C = (°F - 32) ÷ 1.8

Celsius ↔ Kelvin

K = °C + 273.15

°C = K - 273.15

Fahrenheit ↔ Kelvin

K = (°F - 32) × 5/9 + 273.15

°F = (K - 273.15) × 9/5 + 32

Mental Math Tricks

You don’t always need a calculator. Here are shortcuts that get you close enough for everyday situations:

The “Double and Add 30” Trick (C → F)

For a quick Celsius to Fahrenheit estimate:

Double the Celsius temperature
Add 30

Example: 20°C → 2 × 20 + 30 = 70°F (actual: 68°F — close enough!)

This works well for typical weather temperatures (0°C to 35°C). The estimate drifts slightly at extreme temperatures but stays within a few degrees.

The “Subtract 30 and Halve” Trick (F → C)

For a quick Fahrenheit to Celsius estimate:

Subtract 30 from the Fahrenheit temperature
Divide by 2

Example: 80°F → (80 - 30) ÷ 2 = 25°C (actual: 26.7°C — close enough!)

The -40 Crossover

-40 is the magic number where Celsius and Fahrenheit are equal. This is the only point where both scales read the same value. It’s also extremely cold — the kind of temperature you’d only experience in places like Antarctica or Siberia.

Common Reference Points

Memorizing a few key temperatures makes it easy to contextualize any reading:

Reference Point	Celsius	Fahrenheit	Kelvin
Absolute zero	-273.15°	-459.67°	0
Dry ice	-78.5°	-109.3°	194.7
Water freezes	0°	32°	273.15
Refrigerator	4°	39°	277
Comfortable room	21°	70°	294
Body temperature	37°	98.6°	310.15
Hot summer day	38°	100°	311
Water boils (sea level)	100°	212°	373.15

Where Each Scale Is Used

Countries Using Fahrenheit

The United States is the major country that uses Fahrenheit for everyday temperature. A few other territories — including the Bahamas, Belize, the Cayman Islands, and Palau — also use it.

Countries Using Celsius

Virtually everywhere else. The entire scientific community, including in the US, uses Celsius (or Kelvin) for research and technical work.

The UK: A Special Case

The UK officially uses Celsius, but many people — especially older generations — still think in Fahrenheit for warm temperatures. You might hear someone say “it’s in the 70s” on a warm day, even though weather forecasts use Celsius.

Cooking Temperatures

Temperature conversion is crucial in the kitchen, especially when following recipes from different countries:

Oven Temperatures

Description	°C	°F	Gas Mark
Very low	120°	250°	½
Low	150°	300°	2
Medium-low	160°	325°	3
Medium	180°	350°	4
Medium-high	190°	375°	5
High	200°	400°	6
Very high	230°	450°	8

Meat Safety Temperatures

Meat	Safe Internal Temp (°F)	°C
Poultry (whole)	165°	74°
Ground meats	160°	71°
Beef/pork (medium)	145°	63°
Fish	145°	63°

Candy and Sugar Stages

Stage	°F	°C
Thread	230–233°	110–112°
Soft ball	234–240°	112–115°
Firm ball	244–248°	118–120°
Hard ball	250–266°	121–130°
Soft crack	270–290°	132–143°
Hard crack	295–310°	146–154°
Caramel	320–350°	160–177°

Weather Interpretation

Understanding what different temperatures feel like helps you dress appropriately and plan activities:

Celsius Quick Guide (for Fahrenheit users)

°C Range	What It Feels Like
Below -10°	Dangerously cold, stay indoors
-10° to 0°	Bitterly cold, heavy winter gear
0° to 10°	Cold, winter coat needed
10° to 15°	Cool, light jacket
15° to 20°	Mild, comfortable with a sweater
20° to 25°	Warm, pleasant, short sleeves
25° to 30°	Hot, shorts and shade
30° to 35°	Very hot, stay hydrated
Above 35°	Extreme heat, limit outdoor activity

Fahrenheit Quick Guide (for Celsius users)

°F Range	What It Feels Like
Below 0°	Dangerously cold
0° to 32°	Freezing, heavy winter gear
32° to 50°	Cold to cool, jacket needed
50° to 65°	Mild, light layers
65° to 75°	Comfortable, pleasant
75° to 85°	Warm, summer clothes
85° to 95°	Hot, seek shade
Above 95°	Extreme heat warning

Wind Chill and Heat Index

The actual temperature doesn’t tell the whole story. Wind chill makes cold feel colder, and humidity makes heat feel hotter.

Wind Chill Formula (°F)

When temperature is ≤ 50°F and wind speed is > 3 mph: Wind Chill = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Where T = temperature in °F and V = wind speed in mph.

Heat Index

When temperature is ≥ 80°F with significant humidity, the “feels like” temperature can be dramatically higher. At 95°F with 80% humidity, it feels like 133°F.

Convert Temperatures Instantly

Skip the mental math when precision matters. Use our free Temperature Converter to convert between Celsius, Fahrenheit, and Kelvin instantly. It’s perfect for cooking, travel, science homework, or just understanding the weather forecast from another country.

Temperature doesn’t have to be confusing. With these formulas and reference points in your back pocket, you’ll never be caught off guard by a temperature reading — no matter which scale it’s in.