How to Measure Distances Across Rivers or Other Obstacles

measure distances across rivers

Have you ever wanted to measure distances across rivers  or other obstacle without crossing them.  Having a known distance can help you if you are preparing to cross the obstacle, for instance you may need to be sure your rope will reach clear across.  Here are several simple ways of determining the distance.

If you are in the field and need to measure distance, it is always good to know the length of your stride and the number of steps you need to walk either a hundred yards or meters.

One method is to stand on the edge of the river directly facing a known mark on the other bank for example a tree. Take your watch, the kind with hour and minute hands; hold the watch horizontally before you so that the twelve points at the tree and the line joining the nine and the three is parallel to your bank.

Now walk to your right, the direction of the three.  Stop every few steps and make sure that the line from the nine to three is still parallel to the riverbank.  Keep walking until the oak is now at ten thirty, with the nine to three line parallel to the bank.

The distance you have walked is equal to the width of the river.  You can now count your paces and determine the distance across the river or other obstacle.  Just remember this will not work if the river bank curves.  If you don’t have a watch, improvise. Draw one on some paper.


A second method used by Napoleons troops to measure distances across rivers is even simpler. Stand on one bank looking across the river.  Bend your head until your chin touches your chest.  Place your hand on your forehead as if you are shading your eyes, so that the front edge of your palm seems to touch the opposite bank.  Make a quarter turn to either the right or left without moving your hand.  The object the front edge of your hand now touches will be the same distance from you as the distance across the river.  Now pace off the distance to the object and you will know the distance across the river.  This can also be done using the brim of a hat.

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A third method to measure distances across rivers  is Step-Measuring.  This works better than the Napoleon method if the river is wide.  Locate a tree or rock on the other side of the river (A). Place a stick on this side, exactly opposite the rock (B).  Walk along the shore at right angles to AB.  Take any number of steps, up to one hundred.  Place another stick here (C).  Continue walking for half as many steps as before. Place another stick here (D).  At this point, turn away from the river walking at right angles to DB. When you sight stick C and mark A in a straight line, stop. This point is E. DE is then half the distance across the river.  Step it off. Double the distance in line DE and you have the distance across the river.

measure distances across rivers
Step method

Here are some other tips that may help you with measurements in the field.

Test them yourself.

  • At 50 yards, the mouth and eyes of a person can be clearly seen
  • At 100 yards, eyes appear as dots
  • At 200 yards, buttons and details of uniform can still be seen
  • At 300 yards, the face can be seen
  • At 400 yards, the movement of legs can be seen
  • At 500 yards, the color of the uniform can be seen

For distances over these, look for a point that is halfway to the object.  Estimate how far this may be from you and then double it to obtain the distance.

Objects appear nearer than they really are when the sun is bright and shining on the object; when looking across water or snow, and when looking uphill or down.

Objects appear farther off when in the shade; when across a valley; when the background is of the same color; when the observer is lying down or kneeling; when there is a heat haze over the ground.


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