Time, speed, and distance

Model: distance = speed × time

Show your work

1. Time

   $$\mathrm{time}=\mathrm{distance}/\mathrm{speed}$$

   250 NM / 125 kt = 2 h

2. Time en route

   ETE = the time written as hours and minutes

   2 h = 2 h 00 min

The same steps an agent gets from the MCP server with explain: true.

Accuracy: Exact arithmetic; arrival times round to the minute

When to use this: Use this for the arithmetic every leg needs: any two of time, speed, and distance give the third, and a departure time with a UTC offset gives the arrival. It is the quickest way to turn a leg's distance and a groundspeed into an estimate, or to work out the speed a required arrival time implies.

Limitations: It assumes one constant speed over the whole leg, which a climb, a descent, a wind change, or a hold breaks. The speed it works with is whatever you give it, so a true airspeed entered where a groundspeed belongs produces a time that a wind will not honor. Arrival times round to the minute.

Worked example: 250 NM at 125 kt, departing 14:30 at UTC−6. Source: navigation route-geometry scenario: 250 NM at 125 kt is 2 h 00 min.

Review: Not yet independently reviewed by a geodesist.

Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.0, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-19, changed: Time, speed, and distance is stable. It reproduces every one of the 4,800 cells of Bowditch's printed Speed, Time, and Distance table (NGA Pub. 9, Volume II, 2024 edition) to the tenth of a mile the table shows, with one exception: the table prints 6.8 nautical miles for 38 minutes at 10.5 knots, where the arithmetic gives 6.65 and every neighboring cell follows speed times time. The tool gives 6.65, and a test pins the difference. Results are unchanged. Changelog
• 2026-09-19, added: New navigation tools: rhumb lines, cross-track and along-track distance, fly-by turn anticipation, time-speed-distance with arrival times, closest point of approach, and route legs with true and magnetic courses; and the first geometry tool, polygon area on the ellipsoid. Changelog

Checked against: 29 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

• Algorithms for geodesics, Karney, C. F. F., Journal of Geodesy, Vol. 87, No. 1. pp. 43-55.

Terms

UTC: Coordinated Universal Time

The world's civil time standard, kept within 0.9 s of Earth's rotation by leap seconds. Aviation calls it Zulu time, written with a Z. Source: IERS Bulletin C (leap seconds)