Celsius to Fahrenheit Guide: Temperature Conversion Explained

Common Temperature Conversions Reference Chart

Here is a comprehensive reference table of the most commonly searched Celsius to Fahrenheit conversions in the UK, from everyday weather temperatures to cooking and medical contexts.

Celsius (°C)	Fahrenheit (°F)	Context
-10°C	14°F	Severe frost warning in the UK
0°C	32°F	Freezing point of water, icy roads
5°C	41°F	Typical UK winter day
10°C	50°F	Cool spring/autumn day
15°C	59°F	Mild day, light jacket weather
20°C	68°F	Comfortable room temperature
25°C	77°F	Warm UK summer day
30°C	86°F	Hot day, heatwave threshold
35°C	95°F	Extreme UK heat, red warning
37°C	98.6°F	Normal human body temperature
38°C	100.4°F	Fever threshold (NHS guideline)
40°C	104°F	UK record high (2022: 40.3°C)
100°C	212°F	Boiling point of water
160°C	320°F	Low oven / Gas Mark 3
180°C	356°F	Standard baking / Gas Mark 4
200°C	392°F	Hot oven / Gas Mark 6
220°C	428°F	Very hot oven / Gas Mark 7

UK Weather Context: Why Temperature Conversion Matters

The United Kingdom officially uses Celsius for temperature measurement, but many British people still think in Fahrenheit, particularly older generations. The Met Office reports temperatures in Celsius, but newspapers and TV weather presenters often quote both scales during extreme weather events.

Understanding both scales is especially important during UK heatwaves. The Met Office issues amber weather warnings when temperatures exceed 30°C (86°F), and red warnings above 35°C (95°F). In July 2022, the UK recorded its highest-ever temperature of 40.3°C (104.5°F) at Coningsby, Lincolnshire.

During winter, knowing that 0°C equals 32°F helps drivers understand when roads may become icy. The Highways Agency treats roads when temperatures drop below 1°C (33.8°F), and severe weather warnings are issued when temperatures fall below -5°C (23°F).

Cooking Temperature Conversions for UK Kitchens

British recipes often use Celsius and Gas Mark, while many online recipes from the United States use Fahrenheit. Here are the key oven temperature equivalents every UK cook should know:

• Gas Mark 1 (140°C / 275°F) — Very low heat, ideal for slow-cooking meats and drying meringues
• Gas Mark 3 (160°C / 320°F) — Low heat for fruit cakes and casseroles
• Gas Mark 4 (180°C / 350°F) — Standard baking temperature for sponge cakes and biscuits
• Gas Mark 5 (190°C / 375°F) — Roasting vegetables and chicken
• Gas Mark 6 (200°C / 400°F) — Yorkshire puddings and bread
• Gas Mark 7 (220°C / 425°F) — Pizza and crispy roast potatoes
• Gas Mark 9 (240°C / 475°F) — Highest heat for fast-cooking naan bread and flatbreads

Medical Temperature Conversion: NHS Guidelines

NHS guidelines define a fever as a body temperature of 38°C (100.4°F) or above. Normal body temperature ranges from 36.1°C to 37.2°C (97°F to 99°F). When measuring temperature with a thermometer that displays in Fahrenheit, these conversions are essential for accurate health assessment.

For children, the NHS advises seeking medical attention if a baby under 3 months has a temperature of 38°C (100.4°F) or higher, or if a child of any age has a temperature of 39°C (102.2°F) or above that does not respond to paracetamol or ibuprofen.

Understanding the Celsius to Fahrenheit Formula

The formula for converting Celsius to Fahrenheit is straightforward: multiply the Celsius temperature by 9/5 (or 1.8) and then add 32. Written mathematically, this is F = (C × 9/5) + 32. This formula works because the Fahrenheit and Celsius scales have different zero points and different interval sizes. Water freezes at 0°C but at 32°F, meaning there is a 32-degree offset. Additionally, each Celsius degree represents a larger temperature interval than each Fahrenheit degree, specifically 1.8 times larger.

To convert from Fahrenheit back to Celsius, you reverse the formula: subtract 32 from the Fahrenheit temperature, then multiply by 5/9. Written as C = (F - 32) × 5/9. For example, to convert 72°F to Celsius: (72 - 32) × 5/9 = 40 × 5/9 = 22.2°C. This is approximately a comfortable room temperature in the UK.

The two scales intersect at exactly -40 degrees. This means -40°C is identical to -40°F, which is an interesting mathematical fact that occasionally appears in pub quizzes and school science exams across the UK. At this extreme temperature, which has been recorded in northern Scotland during exceptional cold snaps, both thermometer scales read exactly the same value.

A Brief History of Temperature Scales

The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in 1724. He based his scale on three reference points: the freezing point of a brine solution (0°F), the freezing point of pure water (32°F), and the average human body temperature (96°F, later adjusted to 98.6°F). The Celsius scale, originally called the centigrade scale, was developed by Anders Celsius in 1742. He initially set 0 as the boiling point and 100 as the freezing point, but this was later inverted by Carl Linnaeus to the system we use today.

The United Kingdom began its transition from Fahrenheit to Celsius in 1962 when the Met Office switched to reporting temperatures in Celsius. However, the transition was gradual, and many older British citizens still prefer Fahrenheit. Media outlets in the UK often use a clever technique: they report cold temperatures in Celsius (which produces smaller, more alarming numbers like -5°C) and hot temperatures in Fahrenheit (which produces larger, more impressive numbers like 100°F) to maximise the dramatic impact of weather headlines.

Temperature Conversion for UK Travellers

British travellers heading to the United States, Belize, the Cayman Islands, or Palau will encounter Fahrenheit temperatures on local weather reports and thermostats. Knowing a few key benchmarks makes travel more comfortable. A pleasant day at around 75°F is roughly 24°C, which feels similar to a warm British summer day. Air conditioning in American hotels is typically set between 68-72°F (20-22°C). Swimming pool temperatures in Florida or California usually hover around 80-85°F (27-29°C), which is considerably warmer than the typical UK outdoor swimming temperature of 15-18°C (59-64°F).

For UK travellers visiting European destinations, most countries use Celsius, so conversion is unnecessary. However, understanding Fahrenheit remains useful when reading American travel guides, cooking instructions on imported food products, or following international weather reports on apps that default to the Fahrenheit scale.

Frequently Asked Questions

What is the easiest way to convert Celsius to Fahrenheit in my head?

A quick mental trick: double the Celsius number and add 30. For example, 20°C × 2 = 40, then 40 + 30 = 70°F (actual: 68°F). This gives a close approximation within 2-3 degrees for everyday temperatures between 0°C and 35°C.

Why does the UK use Celsius while the US uses Fahrenheit?

The UK officially switched to Celsius in 1962 as part of the metrication programme. The United States remains one of only a few countries worldwide that still primarily uses Fahrenheit for everyday temperature measurement. However, US scientific and medical communities commonly use Celsius.

What temperature should my house be in winter (UK)?

The World Health Organisation recommends a minimum indoor temperature of 18°C (64.4°F) for healthy adults and 21°C (69.8°F) for vulnerable individuals including the elderly and young children. The Energy Saving Trust suggests 18-21°C (64-70°F) as a comfortable range that balances warmth with energy efficiency.

At what temperature do UK schools close?

There is no specific temperature at which UK schools must close, but the Workplace (Health, Safety and Welfare) Regulations 1992 state that indoor temperatures should be "reasonable." The Education Act guidance suggests classrooms should be at least 18°C (64.4°F). Schools may close during extreme heatwaves when classroom temperatures exceed 30°C (86°F) or during severe cold snaps.

What is the difference between Celsius and centigrade?

Celsius and centigrade are the same temperature scale. The name was officially changed from centigrade to Celsius in 1948 by the General Conference on Weights and Measures, to honour Anders Celsius and to avoid confusion with the term centigrade used in some languages to mean one hundredth of a right angle. In everyday UK conversation, both terms are still used interchangeably, although Celsius is the official scientific term.

How accurate are digital thermometers in Celsius and Fahrenheit?

Modern digital thermometers are typically accurate to within 0.1°C or 0.2°F. When converting between scales, rounding can introduce small discrepancies. For medical purposes, the NHS recommends using a digital thermometer that reads in Celsius for the most reliable results. Forehead and ear thermometers can vary by up to 0.5°C depending on technique, so always follow the manufacturer instructions carefully for the most accurate reading.