Free chart-reading tool

Read a nautical chart and measure distance

Use a fictional nautical chart to practice symbols, soundings, hazards and route choice, then learn how to measure distance with dividers and the latitude scale. It is an independent revision aid, not official RYA training or assessment.

Direct answer

To read a nautical chart, check its title, datum, scale and units before interpreting soundings, contours, hazards, buoyage and lights. To measure distance, span the route with dividers and transfer that span to the latitude scale beside the route: one minute of latitude represents one nautical mile. Never measure nautical miles from the longitude scale.

Best for
Chart symbols, depths, hazards, distance and route thinking
Chart type
Fictional teaching chart, not for navigation
Practice mode
Layer toggles, symbol callouts, quiz
Cost
Free, no login required

Symbols, soundings, route choice

Nautical chart reader

Inspect a fictional chart excerpt, separate layers, decode chart symbols, and see how safe tracks combine depth, buoyage, and hazards.

Link to this tool
2m5m081424315772No.2No.1North cardinal0.6RkWk 2.1Fl G 5sTransitCompass SoundFictional teaching chartWGS84 - depths in metresbelow Chart Datum

Learn the concept

How do you measure distance on a nautical chart?

Use dividers to take the straight-line span between two points. Without changing the opening, move the dividers to the latitude scale at the side of the chart and read the minutes of latitude. Each minute represents one nautical mile. On a Mercator chart the scale varies with latitude, so read the scale beside the route rather than at a distant part of the border.

  1. 1Place one divider point on the start and the other on the destination or next waypoint.
  2. 2Move the unchanged span to the latitude scale on the chart border at about the same latitude as the route.
  3. 3Count minutes and decimal minutes of latitude; the same number is the distance in nautical miles.
  4. 4For a bent route, measure each leg separately and add the leg distances.

What should you check before planning a route?

Confirm the chart's edition, corrections, horizontal datum, depth units and scale. Then identify dangers, depth contours, drying areas, aids to navigation and any local notes. A measured line is not automatically a safe route: allow for the vessel's draught, height of tide, under-keel margin, position uncertainty and changing conditions.

Where this fits

  • Day Skipperrelevant
  • Coastal Skipperrelevant
  • Yachtmasterrelevant

Related tools

Chart datum

See how charted depth, height of tide, drying height, and clearance fit together.

IALA Region A buoyage quiz

Practice Region A lateral marks, plus cardinal, safe water, special, and isolated danger marks.

Common questions

Why does one minute of latitude equal one nautical mile?

For practical Mercator chartwork, one minute on the latitude scale represents one nautical mile. The modern international nautical mile is defined as exactly 1,852 metres.

Can you measure nautical miles from the longitude scale?

No. The spacing represented by a minute of longitude changes with latitude. Use the latitude scale beside the route instead.

How do you measure a route with several legs?

Measure each straight leg with dividers, read every span on the nearby latitude scale, then add the leg distances. Record the individual legs as well as the total.