12
kts
45m
45 min
9
nm
The work
Rearranged
T = 60 × D ÷ S
Substituted
T = 60 × 9 ÷ 12 = 45 minutes
Checking against the plain D = S × T? That form needs decimal hours: 0.75 h. Mixing the two — minutes in a formula that wants hours — is the classic way to be out by a factor of 60.
“60 D Street” — the form the exam wants
60 × D = S × T
D in nautical miles, S in knots, T in minutes. Write the triangle down before you touch the numbers: cover the quantity you want and the other two show you whether to multiply or divide.
Ready to try it under exam conditions? Practise navigation questions — every answer cited to the rule it comes from.
Where candidates lose the marks
The relationship is one line of arithmetic. Almost every lost mark on it comes from units rather than algebra.
Minutes vs. hours
60D = ST wants minutes. Plain D = S × T wants decimal hours. Put 45 minutes into the second one and your answer is 60 times too big. Pick a form and keep it.
Nautical vs. statute
Charts, knots and the exam are all nautical — 1,852 m, one minute of latitude. Measure distance against the latitude scale at the side of the chart, never the longitude scale.
Through water vs. over ground
This is the dead-reckoning leg. Set and drift from current, and leeway from wind, are applied afterwards to reach course and speed made good — not folded into this step.
Frequently asked
What is the 60 D Street formula?
60 × D = S × T, where D is distance in nautical miles, S is speed in knots, and T is time in minutes. It is the same relationship as distance = speed × time, rearranged so you can work in minutes instead of decimal hours — which is how Coast Guard problems are posed and how you would time a leg in the wheelhouse. Cover the quantity you want and the remaining two show whether to multiply or divide: D = S × T ÷ 60, S = 60 × D ÷ T, T = 60 × D ÷ S.
Why minutes instead of decimal hours?
Because that is the form the exam asks in. A question gives you '2 hours 45 minutes', not '2.75 hours', and expects an answer in the same shape. Converting to decimals and back is two extra chances to slip. The commonest error on this material is mixing the forms — putting minutes into the plain D = S × T, which wants hours, and landing 60 times out. This calculator takes hours and minutes and shows the decimal equivalent alongside so you can cross-check either way.
How do I work out my ETA?
Find the run time for the leg, then add it to your departure time on the 24-hour clock. Enter a departure time above and the calculator does it, and — importantly — tells you when the arrival crosses midnight into the next day. An ETA of 0300 means very different things depending on whether it is tonight or tomorrow, and a tool that prints the clock time alone invites exactly that mistake.
What is a nautical mile, and why not statute miles?
A nautical mile is 1,852 metres — one minute of latitude, which is what makes it useful: you measure distance off a chart against the latitude scale on the side, not against a separate distance scale. A knot is one nautical mile per hour. Statute miles (5,280 feet) are for road signs; charts, speeds and the exam all use nautical. If you have a distance in statute miles, convert before you start.
Does this account for current or leeway?
No. This is speed through the water against distance run — the dead-reckoning relationship. Set and drift from current, and leeway from wind, are applied separately to get your speed over ground and course made good. Solve the leg here first, then apply the current triangle; do not try to fold them into one step.
Last verified:
Primary sources
- Bowditch, The American Practical Navigator (NGA Pub. No. 9), Ch. 7 — Dead reckoning: the speed, time and distance relationship — Public-domain NGA publication; ingested into our corpus and cited on drill answers.
- NOAA — U.S. Chart No. 1: Symbols, Abbreviations and Terms (distance scales and how nautical miles are measured off a chart) (retrieved 2026-07-28)
- NOAA Ocean Service — What is a nautical mile, and what is a knot? (retrieved 2026-07-28)