How do you calculate flight time from speed and distance?

Flight time = distance ÷ groundspeed. A 92 NM leg at 108 knots groundspeed takes 92 ÷ 108 = 0.85 hours, about 51 minutes. Use groundspeed (true airspeed corrected for wind), not indicated or true airspeed, or headwinds will make every leg run long.

How do pilots check groundspeed in flight?

Time yourself between two checkpoints a known distance apart, then compute groundspeed = distance ÷ time. Flying 5 NM in 2 minutes 32 seconds works out to 118 knots. Comparing that against the planned groundspeed on each leg tells you early whether the winds aloft forecast was right and whether your fuel plan still holds.

What is the 1-in-60 style mental math for leg times?

Divide groundspeed by 60 to get nautical miles per minute: 120 knots is 2 NM per minute, 90 knots is 1.5 NM per minute. Then a 15 NM leg at 120 knots is 7.5 minutes. Working in miles-per-minute is faster in the cockpit than dividing by groundspeed.

Time-Speed-Distance Calculator: Flight Time, Groundspeed & ETA

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Time = distance ÷ groundspeed. Groundspeed = distance ÷ time. Distance = groundspeed × time. One relationship, three directions, and it runs the whole nav log: leg times before takeoff, groundspeed checks between fixes in flight, and the revised ETA when the forecast wind turns out to be fiction. Pick what to solve for below.

Solve for:

Distance (NM)

Leg or trip length from your chart or EFB

Groundspeed (kt)

TAS corrected for wind. Get it from the heading & groundspeed calculator

Time (minutes)

Shown as h:mm in the results

Departure time (optional, for ETA)

Local or Zulu; the ETA uses the same clock

Enter two values to solve the third.

Time –

Pace – NM per minute

One formula, three questions

Everything on a nav log is the same relationship rearranged:

Before takeoff: distance ÷ planned groundspeed = leg time. Add the legs, add the climb, and you have your ETE and fuel requirement.
In flight: distance between two checkpoints ÷ timed minutes = actual groundspeed. This is the number that catches a bad wind forecast an hour before your fuel gauge does.
Diverting: groundspeed × remaining fuel time = how far you can still go. That range circle is the whole point of knowing your groundspeed precisely.

How pilots actually use it in flight

The classic technique is the checkpoint groundspeed check. Pick two features on your chart a known distance apart (5 to 10 NM works well), start a timer over the first, stop it over the second. Five nautical miles in 2:32 is 118 knots. Do this on the first leg of every cross-country: if planned groundspeed was 125 and you measure 108, your ETA, your fuel reserve, and possibly your daylight all just moved, and it is far better to renegotiate the plan over the first checkpoint than over the last one.

The cockpit shortcut is miles per minute: groundspeed ÷ 60. At 90 knots you cover 1.5 NM a minute; at 120, 2 NM a minute. A 14 NM leg at 2 NM per minute is 7 minutes, no calculator needed. This calculator shows the pace figure for exactly that reason.

Worked example

Leg from Renton to Forks, 92.3 NM. The wind triangle gives a groundspeed of 108 knots.

Time = 92.3 ÷ 108 = 0.85 hr ≈ 51 minutes
Departing 12:00Z gives an ETA of 12:51Z
Pace: 108 ÷ 60 = 1.8 NM per minute

At 9.5 GPH that leg also burns about 8.1 gallons, which is the other half of the story: run the time through the fuel & endurance calculator.

Common Questions

Should I use true airspeed or groundspeed for leg times?

Groundspeed. TAS is your speed through the air; the ground does not care. A 120-knot TAS into a 25-knot headwind is a 95-knot groundspeed, and a leg planned on TAS will run 25% long. Compute groundspeed from TAS and the winds aloft with the heading & groundspeed calculator, then bring it here.

How accurate does a planned groundspeed need to be?

Within about 5 knots is fine for planning, because you verify it against reality at the first checkpoint anyway. The discipline that matters is the in-flight check: measured groundspeed replaces planned groundspeed the moment you have it, and every downstream ETA and fuel figure gets revised with it.

Why do my GPS and this calculator disagree?

The GPS reads your instantaneous groundspeed right now; the calculator averages over a leg. Climbs, descents, and wind changes along the route make the two differ. For ETAs, the averaged number over a known distance is the more honest one, which is why the checkpoint timing technique survives in the GPS era.

Related tools and guides

Heading & Groundspeed Calculator

Where the groundspeed number comes from: TAS plus the winds aloft.

Fuel Burn & Endurance Calculator

Turn the leg time into gallons, and gallons into endurance.

The Go/No-Go Decision Framework

A repeatable structure for the decision these numbers feed into.

Your whole route, checked in one pass

FlightDecide runs winds, ceilings, visibility, NOTAMs, fuel, performance, and W&B for your specific flight window and aircraft, and shows the raw data behind every call.

Get FlightDecide on the App Store

Educational tool for flight-planning practice. It is advisory only and not a substitute for your POH, an official weather briefing, or your own judgment as pilot in command (14 CFR 91.3). Sources: FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Ch. 16. Last reviewed: July 17, 2026.