The calculator side of an E6B
The online E6B calculator handles the same core relationships digitally, while the pilot math formulas page shows the equations directly. The circular calculator side of a traditional E6B is a specialized slide rule. It solves multiplication, division, ratios and proportional problems, which makes it useful for time-speed-distance, fuel, unit conversions and many other flight-planning calculations.
Time, speed and distance
Because speed is distance per unit time, the E6B can solve any one of the three when the other two are known. A pilot can set a groundspeed and quickly read travel time for several distances without re-entering the speed each time.
Fuel calculations
The same ratio idea works with fuel flow. Set gallons per hour as a rate and use planned time to estimate fuel burned, or use available fuel to estimate endurance.
Multiplication and division
The rotating scales are logarithmic, so aligning numbers effectively performs multiplication or division through ratios. That is why the device can solve problems that do not look specifically aviation-related.
Unit conversions
Many E6Bs include reference marks for nautical miles, statute miles, kilometers, U.S. gallons, imperial gallons, liters and other common units. Even without dedicated marks, the ratio scales can perform conversions when the conversion factor is known.
Minutes versus decimal hours
A frequent student-pilot error is mixing clock minutes and decimal hours. The E6B's time scale helps relate 30 minutes to 0.5 hour, 15 minutes to 0.25 hour and other values needed for fuel or distance calculations.
Reasonableness still matters
A mechanical E6B typically shows significant digits but not an automatic decimal point. The pilot has to decide whether the answer should be 5, 50 or 500 based on the problem. That habit is also useful when checking an electronic calculator.
Electronic versus manual
An electronic E6B or PilotDesk tool can solve the same relationships faster. The manual device remains valuable for learning how the quantities are connected and for checking whether an electronic result makes sense.
Related PilotDesk guides
Time, speed and distance · Fuel planning · Aviation conversions
Find time, then change the fuel flow
For a 90 NM leg at 120 kt groundspeed, time is 90 ÷ 120 = 0.75 hour, or 45 minutes. On a conventional circular E6B, align the 60-minute rate mark with 120 on the distance scale and read the time opposite 90. Use your model’s instructions for its scale labels.
At 8 US gal/hr, that 45-minute segment uses 8 × 0.75 = 6 gal. Changing fuel flow to 10 gal/hr gives 7.5 gal; it does not change the leg time. Before reading a slide-rule result, decide the expected order of magnitude: 90 NM at 120 kt cannot take 4.5 hours. Verify with the time-speed-distance calculator and the fuel calculator. Taxi, climb and required reserves are separate.
The FAA Pilot’s Handbook of Aeronautical Knowledge, Chapter 16 covers flight-planning calculations and the flight computer.
Mechanical E6B instructions
For your computer’s scales and markings, check the manufacturer’s E6-B instructions. The examples above use the conventional slide-rule and wind-side layout.