Measuring Distance on a Nautical Chart

Distances at sea are measured in nautical miles

  • 1’ (minute) of latitude = 1 nautical mile
  • 1∘ degree of Latitude = 60’ (minute) or 60 nautical miles
  • Land mile = 1609m
  • Nautical mile = 1852m / 1.15 land miles

Some charts (i.e. Imray) have a ‘Scale’ on the chart but if this is not available then you will need to measure the distance from the latitude scale (side) of the chart:

Why do we measure from the side (Latitude Scale) of the Chart?

Distances are always measuring from the Latitude Scale on the Chart NOT the Longitude Scale. As detailed in the image below, the distances between each latitude line are equal, whereas the distances between each Longitude line gets smaller as the lines approach the poles. Only at the Equator are the lines of latitude and longitude at the same distance.  

How to measure distance?

Measure the distance with your dividers, parallel rules, a regular ruler or even a piece of paper!

Take that distance to the latitude scale on the chart to gather the distance in minutes. 

Time Calculations:

Therefore in the example above: 


3.2 n/m (Distance) ÷ 10knots (Speed) = 0.32 x 60 = 19.2 minutes (Time)


D ÷ S = T (in decimals of an hour) x 60 (to convert the decimals into minutes)

Contact us:


Tel: +44 (0) 1202 024111

We DO want to talk to you, but if possible, pls email / send a WhatApp message for the quickest response as we are generally busy teaching... 

Our Locations:

Powerboat & Jetski Courses: Port of Poole Marina
Shorebased Courses: Romany Works, Poole

Post Course eFeedback Form - Click Here

Follow us on Facebook:

Our Trading Names:

RYA Training Centre

Marine Education

'The Superyacht Jetski Specialists'

Superyacht PWC

Superyacht Marine Store

Marine Store EU