Nautical Distance (DR) Calculator
Dead reckoning, or DR, is the foundation of marine navigation: from a known starting point, you project your position using your course, speed and the time elapsed. The distance part of that calculation is a clean product, and this tool computes it. Because a knot is defined as one nautical mile per hour, multiplying your speed in knots by the time in hours gives the distance run in nautical miles directly, with no conversion factor needed. Enter your speed through the water in knots and the time elapsed in hours, and the tool returns the distance covered, the figure you would step off along your course line to advance a DR position on the chart. It also shows the distance covered per minute for quick mental plotting. Real navigation must account for current, leeway and steering error, which is why a DR position is regularly checked against a fix from electronic or visual aids, but the distance run remains the core input. The relationship is exact and perfectly linear. Every figure is computed deterministically from the formula shown below, with a worked example that reconciles exactly to the calculator defaults so you can follow each step.
Distance run is speed in knots x time in hours. At 8 knots for 3 hours, the distance is 24.00 nautical miles, because a knot is one nautical mile per hour.
Nautical distance formula
Distance (NM) = speed x time
speed = boat speed in knots
time = hours elapsed
(1 knot = 1 nautical mile per hour)
Because a knot already means one nautical mile per hour, no conversion is needed: knots times hours gives nautical miles directly. Current and leeway are not included in a basic DR distance.
Worked example
Suppose your speed through the water is 8 knots and 3 hours elapse.
- Distance: 8 x 3 = 24.00 nautical miles
- Per minute: 8 / 60 = 0.13 nautical miles
The distance run is 24.00 nautical miles. These are the calculator's default inputs, so the result matches the widget exactly.
Nautical Distance (DR) Calculator: frequently asked questions
What is dead reckoning?
Dead reckoning is estimating your current position from a known earlier position by applying your course steered, speed and elapsed time. It needs no external fix, which makes it a vital backup, but errors accumulate, so a DR position is regularly corrected with a fix from GPS, bearings or other aids.
Why does knots times hours give nautical miles?
A knot is defined as one nautical mile per hour. So when you multiply knots by hours, the hours cancel and you are left with nautical miles. This clean relationship is why mariners measure speed in knots rather than miles per hour.
Does this account for current?
No. This is the basic distance run through the water. Tidal current and leeway move the vessel relative to the seabed, so the distance and direction made good over the ground can differ. A full DR plot vectors in set and drift to estimate the actual track.
What is speed through the water versus over ground?
Speed through the water is what a log measures relative to the water itself; speed over ground, from GPS, is relative to the seabed and includes the effect of current. For DR distance run, use speed through the water; for distance made good, use speed over ground.
How do I plot the distance on a chart?
Set your dividers to the distance run using the latitude scale at the side of the chart, where one minute of latitude equals one nautical mile, then step it off along your course line from the last position. NOAA produces the nautical charts used for this.
Official sources
- Nautical charts and navigation resources: US National Oceanic and Atmospheric Administration (NOAA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.