Temperature Converter
Convert between Celsius, Fahrenheit and Kelvin instantly. Includes common temperature reference points and conversion formulas.
By Konstantin Iakovlev · Founder, Calks.uk
Last updated: · Verified against HMRC and GOV.UK 2026/27 rates
Celsius
20.00°C
Fahrenheit
68.00°F
Kelvin
293.15 K
Disclaimer
This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.
How It Works
The UK officially uses Celsius for temperature measurement, but Fahrenheit is still commonly understood, especially among older generations and in weather discussions. This converter handles Celsius, Fahrenheit and Kelvin conversions in both directions.
Key reference points: water freezes at 0°C (32°F) and boils at 100°C (212°F). Normal body temperature is approximately 37°C (98.6°F). The NHS considers a fever to be 38°C or above. Oven temperatures are often given in Celsius with a gas mark equivalent in UK recipes.
Celsius to Fahrenheit conversion. °F = (°C × 9/5) + 32. °C = (°F − 32) × 5/9. Key anchors: −40°C = −40°F (only meeting point); 0°C = 32°F (water freezes); 16°C = 60.8°F (cool day); 20°C = 68°F (room temp); 25°C = 77°F; 30°C = 86°F (hot); 37°C = 98.6°F (body); 100°C = 212°F (water boils at sea level). UK officially Celsius since 1972 but Fahrenheit still mentioned for emphasis ('a sweltering 90°F!').
Kelvin and absolute zero. Kelvin scale: K = °C + 273.15. Absolute zero = −273.15°C = 0 K (theoretical lower limit, never achieved). Water freezes 273.15 K; body temp 310 K; water boils 373.15 K. Used in science (physics, chemistry, astronomy). Kelvin same magnitude as Celsius — no degree symbol (just 'K'). UK university physics uses Kelvin for thermodynamics; everyday Celsius. Stars rated by colour temperature in Kelvin: warm white bulb 2700K; daylight bulb 6500K; sun 5778K.
UK climate temperature averages. UK record high: 40.3°C (104.5°F) at Coningsby, Lincs, 19 July 2022 — first UK day over 40°C. Record low: −27.2°C (−17.0°F) at Braemar/Altnaharra (Scotland). Average UK summer day: 16-22°C. Average winter day: 3-8°C. London 1.5-2°C warmer than rural surrounds (urban heat island). Scotland 2-4°C cooler than southern England. Climate change: UK warmed ~1.0°C since 1980; 10 hottest UK years all since 2002.
Body temperature in Celsius and Fahrenheit. Normal: 36.1-37.2°C (97-99°F). Fever NHS definition: ≥38.0°C (100.4°F). High fever: ≥39.5°C (103.1°F). Hyperthermia/heatstroke: >40°C (104°F) — medical emergency. Hypothermia: <35°C (95°F); severe <32°C. Body temp varies daily: lowest 4am, peak 6pm (~0.5°C diurnal swing). Women's basal temp rises 0.3-0.5°C after ovulation. Children typically run 0.3-0.5°C warmer than adults.
Cooking and oven temperatures. Gas Mark 1 = 140°C / 275°F; Gas 4 = 180°C / 350°F (most baking); Gas 6 = 200°C / 400°F; Gas 9 = 240°C / 475°F (pizza, very hot). Fan-assisted ovens run 20°C hotter at same dial setting — reduce by 20°C when adapting recipes. Sugar stages: soft ball 116°C (240°F); hard crack 149°C (300°F); caramel 170°C (340°F). Meat doneness: rare 52°C (125°F); medium-rare 57°C (135°F); medium 63°C (145°F); well-done 71°C+ (160°F+).
Example: Common temperature conversions
- 20°C = 68°F (comfortable room temperature)
- 37°C = 98.6°F (body temperature)
- 180°C = 356°F / Gas Mark 4 (moderate oven)
- −40°C = −40°F (the point where both scales meet)
Frequently Asked Questions
- Celsius to Fahrenheit — exact formulas.
- °F = (°C × 9/5) + 32. °C = (°F − 32) × 5/9. Useful anchors: −40°C = −40°F (only point they meet); 0°C = 32°F (water freezes); 20°C = 68°F (room temp); 37°C = 98.6°F (body); 100°C = 212°F (water boils at sea level). Kelvin: K = °C + 273.15 (absolute zero = −273.15°C = 0 K). UK officially uses Celsius since 1972 but weather forecasts sometimes still mention Fahrenheit ('a sweltering 90°F!') for emphasis.
- UK weather temperature records.
- UK record high: 40.3°C (104.5°F) at Coningsby, Lincs, 19 July 2022 — first time UK passed 40°C. Record low: −27.2°C (−17.0°F) at Braemar/Altnaharra (1895, 1982, 1995). Average UK summer: 16-20°C; winter: 3-6°C. London ~1.5°C warmer than rural surrounds (urban heat island). Scotland 2-3°C cooler than southern England. Climate trend: UK has warmed ~1.0°C since 1980; 10 hottest years on record all since 2002.
- Body temperature interpretation.
- Normal body temperature: 36.1-37.2°C (97-99°F). Fever: ≥38.0°C (100.4°F) per NHS. High fever: ≥39.5°C (103.1°F). Hyperthermia (heat stroke): >40°C — medical emergency. Hypothermia: <35°C (95°F); severe <32°C. Body temp varies through day — lowest at 4am, peak 6pm (~0.5°C swing). Women's basal temp rises 0.3-0.5°C after ovulation. Thermometer placement: oral usually 0.5°C below rectal, axillary (armpit) ~1°C below.
- Cooking and oven temperature conversions.
- Gas Mark 1 = 140°C / 275°F; Gas 4 = 180°C / 350°F (most baking); Gas 6 = 200°C / 400°F; Gas 9 = 240°C / 475°F (pizza, very hot). Fan-assisted ovens run 20°C hotter — reduce dial by 20°C when adapting recipes (180°C conventional → 160°C fan). Sugar stages: soft ball 116°C, hard crack 149°C, caramel 170°C. Meat: rare 52°C, medium-rare 57°C, medium 63°C, well-done 71°C+. Food safety: hold hot food above 63°C, cold below 5°C — 'danger zone' is 5-63°C.