Online E6B
Flight Computer

An E6B is a circular slide rule used by pilots for over 80 years to perform essential flight planning calculations. It has two sides: the wind side solves the wind triangle (ground speed, wind correction angle, true heading) and the calculator side handles speed/distance/time, fuel burn, unit conversions, true airspeed, and density altitude. This online calculator replicates all of those functions using exact digital computation instead of graphical approximation.

Wind Correction Angle (WCA) is calculated using the formula WCA = arcsin(Wind Speed × sin(Wind Direction − True Course) / TAS). You need four inputs: your True Airspeed from POH performance charts, the True Course plotted on your chart, the Wind Direction (the direction the wind blows FROM) from winds aloft forecasts, and the Wind Speed in knots. The WCA tells you how many degrees to crab into the wind to maintain your desired course over the ground.

True Airspeed (TAS) is your actual speed through the air mass, corrected for altitude and temperature. Ground Speed (GS) is your speed over the ground, which is TAS adjusted for wind. A headwind reduces ground speed below TAS; a tailwind increases it. Always use ground speed not TAS for ETA, fuel, and distance calculations because ground speed determines how fast you actually cover distance over the earth's surface.

First calculate Pressure Altitude: Field Elevation + ((29.92 − altimeter setting) × 1000). Then find the ISA standard temperature at that altitude: 15°C − (2°C × thousands of feet). Finally, Density Altitude = Pressure Altitude + (120 × (actual temperature − ISA temperature)). For example, at 5,000 ft elevation with 35°C OAT and 29.82 altimeter: PA = 5,100 ft, ISA = 5.1°C, DA = 5,100 + (120 × 29.9) = 8,688 ft.

This online calculator uses the exact same formulas as the FAA-approved CX-2 and CX-3 electronic flight computers. You can use it to study and practice E6B problems. For the actual written exam at a testing centre, you will need to bring a physical E6B (manual or electronic) online tools are not permitted during the exam. However, practising with this calculator builds the understanding needed to use any E6B effectively.

Density altitude represents the altitude at which the atmosphere behaves in terms of air density. Higher density altitude means thinner air, which reduces engine power output, propeller efficiency, and wing lift simultaneously. This results in longer takeoff rolls, reduced climb rates, and higher true airspeeds for the same indicated airspeed. A runway at 2,000 ft elevation on a hot day (35°C) can have a density altitude of 5,000+ ft, meaning the aircraft performs as if it were at 5,000 ft on a standard day.

One nautical mile equals 1.15078 statute miles, or 1.852 kilometres. To convert NM to SM, multiply by 1.15078. To convert SM to NM, multiply by 0.86898. Aviation uses nautical miles for distance and knots (nautical miles per hour) for airspeed because one nautical mile equals one minute of latitude, making chart navigation mathematically simpler.

Under FAA regulations (14 CFR 91.151), VFR day flights require enough fuel to reach the destination plus 30 minutes of flight at normal cruise. VFR night flights require 45 minutes reserve. IFR flights (14 CFR 91.167) require fuel to the destination, then to the alternate, plus 45 minutes. Under EASA, similar requirements apply with variations depending on the type of operation. This calculator shows remaining reserve fuel so you can verify compliance before departure.