°C ↔ °F Converter
Convert between Celsius and Fahrenheit. Aviation METARs and TAFs report temperature in Celsius, while some US pilots are more familiar with Fahrenheit.
Formula
°F = (°C × 9/5) + 32 °C = (°F − 32) × 5/9
Multiply Celsius by 9/5 then add 32 to get Fahrenheit. Subtract 32 from Fahrenheit then multiply by 5/9 to get Celsius.
Reference Table
| °C | °F | Aviation Context |
|---|---|---|
| -40 | -40 | C and F are equal at this point |
| 0 | 32 | Freezing level — icing risk begins |
| 15 | 59 | ISA sea-level standard temperature |
| 30 | 86 | Hot day — significant DA increase |
| 40 | 104 | Extreme heat — major performance reduction |
Aviation Context
Aviation uses Celsius for outside air temperature (OAT), which directly affects density altitude, true airspeed, and engine performance. The ISA standard temperature at sea level is 15°C (59°F), decreasing approximately 2°C per 1,000 ft. Temperatures above ISA increase density altitude and degrade aircraft performance.
Why This Matters in Aviation
Outside air temperature drives density altitude, and density altitude drives takeoff distance, climb rate, and true airspeed. A pilot reading a METAR that reports temperature in Celsius needs to relate it to performance charts, some of which are laid out in Fahrenheit. On a hot day, converting and understanding the temperature helps a pilot anticipate a longer ground roll and a weaker climb, exactly the situation the FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25) warns about for high-density-altitude operations. Knowing that ISA sea-level temperature is 15 degrees C (59 degrees F) gives a quick baseline for judging whether conditions are hotter or colder than standard.
Understanding This Conversion
Temperature is central to aircraft performance, and aviation weather worldwide reports it in degrees Celsius. Pilots in the United States, however, live in a Fahrenheit world outside the cockpit, so the ability to move between the two scales quickly is a daily necessity. This converter bridges the gap, but the deeper value is being able to feel what a Celsius temperature means for density altitude, icing, and comfort without stopping to compute.
A METAR gives temperature and dewpoint in Celsius, performance charts assume Celsius or reference the standard 15-degree-Celsius day, and icing thresholds are defined around zero Celsius. Fluency with the conversion lets a pilot who thinks natively in Fahrenheit translate these aviation values into an intuitive sense of the conditions.
Why the Unit Matters in Aviation
Aviation adopted Celsius for temperature because it aligns with the international standard atmosphere and makes the freezing point a clean zero, which matters enormously for icing. When a METAR reports a temperature of 2 degrees Celsius with visible moisture, the proximity to zero is an immediate icing flag that the Fahrenheit equivalent of about 36 degrees would obscure. Thinking in Celsius keeps the freezing reference front and center.
Temperature drives density altitude, and the standard-atmosphere reference of 15 degrees Celsius at sea level is the baseline against which performance charts are built. Every degree Celsius above standard raises density altitude and degrades performance, so pilots learn to compare the reported Celsius temperature against the standard value for their elevation. This is far easier when temperature is habitually read in Celsius rather than converted back and forth.
Common Conversion Mistakes to Avoid
The most common mistake is applying only the multiply-or-divide step and forgetting the 32-degree offset. Celsius to Fahrenheit is multiply by 9/5 and then add 32; leaving out the offset can put an answer wildly off, especially near the temperatures that matter for icing and performance.
Another error is losing the sign near freezing. A temperature of minus 5 degrees Celsius is 23 degrees Fahrenheit, still below freezing, but a careless conversion can flip the pilot's sense of whether conditions are above or below zero, which is exactly the distinction that governs icing risk.
Quick-Reference Scenarios
Judging icing risk from a METAR
A report shows 1 degree Celsius with light rain. Recognizing that this is just above freezing, and that cooling with altitude will quickly cross zero, tells you icing is a live concern without needing to convert to Fahrenheit at all.
Estimating density altitude
The temperature is 30 degrees Celsius at a 3,000-foot field where standard temperature is about 9 degrees. The 21-degree excess warns of a substantial density-altitude penalty, a judgment made directly in Celsius.
Briefing a passenger
A passenger asks how cold it will be at altitude. Converting minus 10 degrees Celsius to about 14 degrees Fahrenheit makes the answer meaningful to someone who thinks in Fahrenheit.
Related Standards & Regulations
The International Standard Atmosphere defines a sea-level temperature of 15 degrees Celsius and a lapse rate of about 2 degrees Celsius per 1,000 feet, the reference underlying nearly all performance and altimetry work. Aviation weather reports worldwide use Celsius accordingly.
The conversion is exact: degrees Fahrenheit equal degrees Celsius times nine-fifths plus thirty-two. Because the relationship is linear with an offset, both the scale factor and the offset must be applied for any correct conversion.
Related Reading & Tools
Frequently Asked Questions
Want AI explanations, checkride questions, and saved calculations?
FlightCalculators.com is powered by the same team behind SkeyeMentor — the AI-powered FAA ground school. Try SkeyeMentor free.
Try SkeyeMentor Free