Time, speed and distance for pilots
Time, speed and distance math appears everywhere in flight planning. It is used to estimate leg time, groundspeed, distance remaining, fuel burn and arrival time. The three quantities are directly related, so knowing any two lets you solve for the third.
The three core formulas
Distance = speed × time. Time = distance ÷ speed. Speed = distance ÷ time. For aviation calculations, speed is commonly in knots, distance in nautical miles and time in hours. Keep the units consistent before solving.
90 NM at 120 knots
If a leg is 90 NM and groundspeed is 120 knots, time is 90 ÷ 120 = 0.75 hour, or 45 minutes. Multiplying decimal hours by 60 converts the answer to minutes.
24 minutes at 105 knots
If groundspeed is 105 knots and the airplane flies for 24 minutes, first convert 24 minutes to 0.4 hour. Distance is 105 × 0.4 = 42 NM.
Use groundspeed for ETA
When estimating time over the ground, use groundspeed rather than true airspeed. Wind can make groundspeed very different from TAS. Rechecking the math with an updated groundspeed is a useful way to refine an ETA in flight.
Quick mental checks
At 120 knots the airplane travels about 2 NM per minute. At 90 knots it travels about 1.5 NM per minute. These simple relationships make it easier to catch a calculator entry that is obviously wrong.
Connect time to fuel
Once flight time is known, fuel used can be estimated from time × fuel flow. That makes time-speed-distance math a foundation for fuel planning as well as navigation.
Related PilotDesk tools
NM per minute · Wind triangle · Route planner