A Celsius to Fahrenheit calculator converts a temperature from the metric scale used almost everywhere outside the United States to the Fahrenheit scale used inside it. Enter a value in degrees Celsius and the calculator returns the Fahrenheit equivalent using °F = °C × 9 ÷ 5 + 32.
Useful for travelers reading European or Asian weather forecasts, cooks converting recipes between metric and US measurements, scientists working across both systems, and anyone moving between the two countries that still use Fahrenheit (the United States and a handful of Caribbean nations).
Key takeaway
Celsius and Fahrenheit are linear scales with different anchor points and different step sizes. Celsius pegs water's freezing and boiling points at 0° and 100° (a clean 100-degree span); Fahrenheit pegs them at 32° and 212° (a 180-degree span). The conversion formula has to handle both the offset and the slope, that's why it's × 9/5 + 32, not just one or the other.
How it's calculated
The conversion:
°F = °C × 9 ÷ 5 + 32
The × 9/5 (or 1.8) handles the slope difference: Fahrenheit degrees are smaller than Celsius degrees, so each Celsius degree is worth 1.8 Fahrenheit degrees. The + 32 handles the offset: Fahrenheit's zero is below Celsius's zero by 32°F worth of distance.
A useful identity to remember: at −40°, the two scales are equal (−40°C = −40°F). It's the only point where they cross. Below it, Fahrenheit numbers are higher than Celsius; above it, the gap grows the warmer it gets.
Source: Standard temperature conversion, °F = °C × 9 ÷ 5 + 32
Examples
20°C, a mild spring day
- Temperature 20 °C
20°C converts to 68°F, a comfortable spring or autumn temperature. Mental shortcut: double 20 to get 40, add 30 → ~70°F (close to the real 68). Within US rooms, 68-72°F is the standard "comfortable" range, which maps to roughly 20-22°C.
30°C, hot summer afternoon
- Temperature 30 °C
30°C is 86°F, properly hot in most climates, the kind of day where you'd reach for shade or the AC. Doubling-plus-30 estimates 90°F; the real answer is 4° lower. The shortcut is good for quick reads but drifts a couple degrees off in summer ranges.
Frequently asked questions
How do I convert Celsius to Fahrenheit in my head?
Use the double-and-add-30 shortcut: take the Celsius value, multiply by 2, then add 30. So 20°C → 40 + 30 = 70°F (actual: 68°F, close enough). 25°C → 50 + 30 = 80°F (actual: 77°F). The shortcut gets within a few degrees of the real answer for everyday temperatures, which is usually plenty for travel planning.
Why is the formula × 9/5 + 32, not just × 2 + 30?
Because the scales have different step sizes. A 1°C change is exactly 1.8°F (= 9/5), so multiplying by 9/5 captures the precise slope. The +32 accounts for the offset between the two zero points (water freezes at 32°F). The double-and-add-30 mental shortcut works because 2 ≈ 1.8 and 30 ≈ 32, but it's an approximation, not the exact formula.
At what temperature do Celsius and Fahrenheit match?
At −40°, the two scales give the same number, it's the only point where °C = °F. Above that point, Fahrenheit numbers are larger; below, Fahrenheit numbers are still larger but the gap is small. Memorize "−40 is −40" and you have a permanent anchor point for cold-weather conversions.
Which countries still use Fahrenheit?
The United States is the main holdout. The Bahamas, Belize, the Cayman Islands, Palau, the Federated States of Micronesia, the Marshall Islands, and Liberia also still use Fahrenheit, often alongside Celsius. Everywhere else, including the UK and Canada in everyday weather use, is firmly on Celsius. The US National Weather Service is the most-cited Fahrenheit source globally.