Time, speed and distance calculator
Distance equals speed multiplied by time. Almost every other navigation calculation is built on it, and most in flight arithmetic comes back to it.
Calculator
This is an educational and planning aid. Use current official weather, your aircraft flight manual, and the rules that apply to your flight before you act on any figure here. See the aviation disclaimer.
What the result means
Pick which of the three you want and supply the other two. The calculator rearranges the relationship for you and handles the unit conversions, which is where most errors creep in.
Use groundspeed, not airspeed. The relationship describes movement over the ground, so the wind has to be in the number already.
When this is useful
- Working out leg times during flight planning, which then feed the fuel calculation.
- In flight, checking your groundspeed against a known distance between two fixes and the time it took.
- Revising an estimate when the wind turns out different from the forecast and the arrival time moves.
How it is calculated
The three forms are distance divided by speed for time, speed multiplied by time for distance, and distance divided by time for speed. The calculator converts everything into knots, nautical miles and hours first, then converts the answer back.
distance = groundspeed x time
Worked example
- Groundspeed
- 120 kt
- Distance
- 90 NM
- Solve for
- Time
The leg takes 45 minutes.
Check: At 120 kt you cover 2 NM every minute, so 90 NM takes 45 minutes. The mental arithmetic and the calculator agree exactly.
Limitations
- It assumes a constant groundspeed for the whole period. A climb, a descent or a wind shift all break that assumption.
- It knows nothing about taxi, holding, or the approach at the far end. Those have to be added separately.
Common mistakes
- Using true airspeed where groundspeed is needed. Into a 30 kt headwind that mistake makes every leg time optimistic.
- Mixing units, such as a distance in kilometres against a speed in knots. Use the unit selectors instead of converting mentally.
- Reading a decimal answer as hours and minutes. An answer of 1.5 hours is 1 hour 30 minutes, not 1 hour 50.
Sources
- Pilot's Handbook of Aeronautical Knowledge, navigation chapter , US Federal Aviation Administration