Temperature Converter
Temperature Conversions (°C, °F, K): A Friendly, Practical Guide
Need to switch between Celsius (°C), Fahrenheit (°F), and Kelvin (K) quickly and accurately? This guide walks you through everything: the exact formulas, why the scales exist, common mistakes to avoid, quick reference tables, and real-life examples (cooking, weather, labs, travel). Use the Temperature Converter on this page to get instant results— and come back to the explanations below whenever you want to understand the “why” behind the numbers.
- Three core scales: Celsius Fahrenheit Kelvin.
- Essentials: °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9, K = °C + 273.15.
- Kelvin is an absolute scale starting at absolute zero; it’s the scientific default.
- For oven/cooking and weather, use our quick tables to sanity-check results.
How temperature works
Temperature measures how much the particles in a substance are jiggling around on average. More jiggle (higher kinetic energy) → higher temperature. If particles barely move at all, you’re approaching absolute zero (−273.15 °C, −459.67 °F, 0 K), the theoretical point where random motion hits the minimum. Different scales just label these energy levels with different zero points and step sizes.
Meet the three main scales
Celsius (°C)
Built around water: 0 °C at the freezing point and 100 °C at the boiling point (at 1 atm pressure). Most of the world uses Celsius for daily life and weather reports. It’s convenient, decimal, and ties to familiar physical reference points.
Fahrenheit (°F)
Still common in the United States for weather, cooking, and thermostats. Its scale spreads typical weather temperatures (say −10 °C to 35 °C) across a broader numerical range (14 °F to 95 °F), which some people find more granular for comfort settings.
Kelvin (K)
The scientific standard. Kelvin has the same step size as Celsius (1 K = 1 °C) but shifts the zero point to absolute zero. That makes it perfect for formulas in physics and chemistry, where absolute temperature matters.
Core formulas with worked examples
1) Celsius ⇄ Fahrenheit
°F = °C × 9/5 + 32
°C = (°F − 32) × 5/9
Example (room temperature): 21 °C → °F?
21 × 9/5 + 32 = 69.8 °F (≈ 70 °F)
Example (fever): 101.3 °F → °C?
(101.3 − 32) × 5/9 = 38.5 °C
2) Celsius ⇄ Kelvin
K = °C + 273.15
°C = K − 273.15
Example: 25 °C → K = 298.15 K.
310 K → °C = 36.85 °C.
3) Fahrenheit ⇄ Kelvin
K = (°F + 459.67) × 5/9
°F = K × 9/5 − 459.67
Example: 68 °F → K?
(68 + 459.67) × 5/9 = 293.15 K.
Quick conversion tables
Common points & everyday references
| Situation | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Extremely cold day | −40 | −40 | 233.15 |
| Freezing point of water | 0 | 32 | 273.15 |
| Room temperature (typical) | 21 | 69.8 | 294.15 |
| Body temperature (average) | 37 | 98.6 | 310.15 |
| Water boiling point (1 atm) | 100 | 212 | 373.15 |
| Very hot oven | 220 | 428 | 493.15 |
Fahrenheit ⇄ Celsius (every 10 °F step)
| °F | °C | °F | °C | °F | °C |
|---|---|---|---|---|---|
| 32 | 0.0 | 72 | 22.22 | 112 | 44.44 |
| 42 | 5.56 | 82 | 27.78 | 122 | 50.00 |
| 52 | 11.11 | 92 | 33.33 | 132 | 55.56 |
| 62 | 16.67 | 102 | 38.89 | 142 | 61.11 |
Remember: exact °C values may go to many decimals; round to the precision you need.
Beyond the big three: Rankine & Réaumur
Rankine (°R) is essentially the Fahrenheit version of Kelvin. It starts at absolute zero and uses Fahrenheit-sized degrees. Handy in thermodynamics (especially older U.S. engineering textbooks).
- °R = °F + 459.67
- °R = K × 9/5
Réaumur (°Ré) divides the freezing-to-boiling interval of water into 80 parts. It shows up in some historical European references.
- °Ré = °C × 4/5
- °Ré = (°F − 32) × 4/9
Everyday uses: kitchen, weather, travel
Cooking & baking
Recipes switch scales all the time: European blogs may use °C, U.S. sites often use °F. If your oven only shows one scale, convert the target temperature and round to the nearest setting your oven supports. For delicate bakes, use an oven thermometer: real oven temps swing, so a ±10 °C (±18 °F) drift is common.
| Kitchen target | °C | °F |
|---|---|---|
| Slow roast | 150 | 302 |
| Moderate oven | 180 | 356 |
| Hot oven | 200 | 392 |
| Very hot oven | 220 | 428 |
Weather & clothing
A quick mental shortcut: to get °F from °C, double and add 30 (works roughly from 0–30 °C). Example: 20 °C → about 70 °F. Not exact, but close enough to decide if you need a jacket.
Travel
Switching countries? Use the converter to plan outfits and gear. 5 °C rainy in spring can feel chilly without layers; 30 °C in a dry climate feels different from 30 °C with high humidity.
Science & industry notes (concise)
- Chemistry & physics: use Kelvin in equations that involve temperature ratios or absolute energy.
- Sensors: thermistors, RTDs, and thermocouples all have tolerances. Check your device’s spec sheet for typical error (±0.1 °C to ±2 °C or more).
- Calibration: for critical work, calibrate against known references (ice bath near 0 °C, boiling water ~100 °C at 1 atm, or certified blocks).
Accuracy, rounding & common mistakes
- Keep units straight. Mixing °F and °C is the #1 source of wild results.
- Be mindful of decimals. Cooking can tolerate ±5 °C error; lab work often can’t.
- Use consistent precision. If your input is 2 decimals, show outputs to 2–3 decimals unless your context needs more.
- Watch altitude. Boiling point changes with pressure; at high elevations, water boils below 100 °C.
- Don’t forget the +32 and ×9/5 steps. A common slip is to multiply without adding 32 when going °C → °F.
Classroom-style Worked Examples (Step by Step)
Example 1 — Convert 30 °C to °F
Formula: °F = °C × 9/5 + 32
30 × 9/5 + 32 = 54 + 32 = 86 °F.
Example 2 — Convert 86 °F to °C
Formula: °C = (°F − 32) × 5/9
(86 − 32) × 5/9 = 54 × 5/9 = 30 → 30 °C.
Example 3 — Convert 25 °C to K
Formula: K = °C + 273.15
25 + 273.15 = 298.15 K.
Example 4 — Convert 310 K to °C and °F
°C = 310 − 273.15 = 36.85 °C.
°F = 36.85 × 9/5 + 32 = 66.33 + 32 = 98.33 °F (≈ 98.3 °F).
Example 5 — Below freezing: −10 °C to °F
°F = (−10) × 9/5 + 32 = −18 + 32 = 14 °F.
Example 6 — Body temperature: 101.3 °F to °C
(101.3 − 32) × 5/9 = 69.3 × 5/9 = 38.5 °C (fever range).
Example 7 — Lab example: 77 °F to K
K = (°F + 459.67) × 5/9 = (77 + 459.67) × 5/9 = 536.67 × 5/9 = 298.15 K.
Example 8 — Thermodynamics note (Rankine)
Rankine uses Fahrenheit-sized degrees with absolute zero at 0 °R.
- °R = °F + 459.67 (e.g., 77 °F → 536.67 °R)
- °R = K × 9/5 (e.g., 298.15 K → 536.67 °R)
Example 9 — Historical scale (Réaumur)
°Ré = °C × 4/5, so 25 °C → 20 °Ré. Reverse: °C = °Ré × 5/4.
Example 10 — Mental check
20 °C → double (40) + 30 ≈ 70 °F (exact: 68 °F). Good quick estimate!
Practice Set (with Hidden Solutions)
Try these on your own. Click “Show answers” to reveal detailed solutions.
- Convert 12 °C to °F.
- Convert 59 °F to °C.
- Convert −25 °C to °F.
- Convert 451 °F to °C (baking high heat).
- Convert 0 °C to K.
- Convert 373.15 K to °C and °F.
- Convert 95 °F to K.
- Convert 310.15 K to °F.
- Weather: 5 °C morning → °F?
- Freezer: −4 °F → °C?
- Lab: 250 K → °C and °F.
- Room: 68 °F → °C and K.
- Hot day: 40 °C → °F.
- Water pasteurization: 72 °C → °F.
- Dry ice surface: −78.5 °C → °F.
- Réaumur: 24 °Ré → °C.
- Rankine: 540 °R → °F and K.
- Human body: 99.5 °F → °C.
- Hot oven: 220 °C → °F.
- Very cold day: −40 °F → °C and K.
Show answers
- 12 × 9/5 + 32 = 21.6 + 32 = 53.6 °F.
- (59 − 32) × 5/9 = 27 × 5/9 = 15 °C.
- (−25) × 9/5 + 32 = −45 + 32 = −13 °F.
- (451 − 32) × 5/9 = 419 × 5/9 = 232.78 °C (≈ 233 °C).
- 0 + 273.15 = 273.15 K.
- 373.15 K → °C = 100; °F = 100 × 9/5 + 32 = 212 °F.
- K = (95 + 459.67) × 5/9 = 554.67 × 5/9 = 308.15 K.
- °F = 310.15 × 9/5 − 459.67 = 558.27 − 459.67 = 98.60 °F.
- 5 × 9/5 + 32 = 9 + 32 = 41 °F.
- (−4 − 32) × 5/9 = −36 × 5/9 = −20 °C.
- 250 K → °C = −23.15; °F = (−23.15 × 9/5) + 32 = −41.67 + 32 = −9.67 °F.
- 68 °F → °C = 20; K = 293.15 K.
- 40 × 9/5 + 32 = 72 + 32 = 104 °F.
- 72 × 9/5 + 32 = 129.6 + 32 = 161.6 °F.
- −78.5 × 9/5 + 32 = −141.3 + 32 = −109.3 °F.
- °C = 24 × 5/4 = 30 °C.
- °F = 540 − 459.67 = 80.33 °F; K = 540 × 5/9 = 300 K.
- (99.5 − 32) × 5/9 = 67.5 × 5/9 = 37.5 °C.
- 220 × 9/5 + 32 = 396 + 32 = 428 °F.
- −40 °F = −40 °C; K = −40 + 273.15 = 233.15 K.
Expanded Oven & Gas Mark Conversion
Gas Mark values are traditional UK settings. Fan-assisted ovens typically run ~20 °C lower for the same effect. Always check your oven manual and use an oven thermometer if precision matters. Values below are standard approximations.
| Description | Gas Mark | Conventional °C | Fan °C (≈ −20) | °F |
|---|---|---|---|---|
| Very cool / Very slow | ¼ | 107 | 90 | 225 |
| Very cool / Very slow | ½ | 121 | 100 | 250 |
| Cool / Slow | 1 | 135 | 115 | 275 |
| Slow | 2 | 149 | 130 | 300 |
| Moderate | 3 | 163 | 145 | 325 |
| Moderate | 4 | 177 | 160 | 350 |
| Moderately hot | 5 | 191 | 170 | 375 |
| Hot | 6 | 204 | 185 | 400 |
| Very hot | 7 | 218 | 200 | 425 |
| Very hot | 8 | 232 | 210 | 450 |
| Extremely hot | 9 | 246 | 225 | 475 |
Quick oven reference (rounded targets)
| Target | °C | °F | Gas |
|---|---|---|---|
| Slow roast | 150 | 302 | 2 |
| Moderate baking | 180 | 356 | 4 |
| Hot oven (pizza, flatbreads) | 220 | 428 | 7–8 |
FAQ
What are the exact formulas for °C, °F, and K?
°F = °C × 9/5 + 32; °C = (°F − 32) × 5/9; K = °C + 273.15; K = (°F + 459.67) × 5/9.
Which scale should I use?
Daily life: °C in most countries, °F in the U.S.; science & engineering: Kelvin for absolute temperature calculations.
Why is Kelvin not written with a degree sign?
Kelvin is an absolute thermodynamic temperature scale; its unit is just K (not °K).
How accurate is a typical kitchen oven?
It can drift by ±10 °C (±18 °F) or more. Use a separate oven thermometer when precision matters.
What’s the fastest way to sanity-check a result?
Use the mental rule of thumb (double °C and add 30 ≈ °F) or compare against the quick tables above.
Use the converter tool above for instant results. Bookmark this guide to understand the numbers you see.