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Contour Interval Calculator

Work out contour interval instantly with clear inputs, formula shown and shareable results.

About Contour Interval Calculator

Contour interval is the elevation difference divided by the number of gaps, which is one less than the number of lines counted. 250 m across five index contours gives 50 m intervals. Conventional intervals scale with the map: about 10 m at 1:25,000 and 20 m at 1:50,000, though relief and terrain type shift the choice.

Formulas

Contour interval

interval = elevation difference / (contours counted - 1)

Map distance

1 km on the ground = 100000 / scale denominator cm on the map

Worked example

With the default values below, Contour Interval Calculator returns Contour Interval of 62.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Map scale denominatorminimum 1
25,000
Index contours countedminimum 1
5
Elevation difference between themminimum 0 m
250 m

Results

Contour Interval
62.50 m
Intervals Between The Contours
4
Conventional Interval For That Scale
12.5 m
One Kilometre On The Map
4.00 cm

Step by step

  1. 1Values used
  2. 2Contour interval
  3. 3Map distance
  4. 4Contour Interval= 62.50 m
  5. 5Intervals Between The Contours= 4
  6. 6Conventional Interval For That Scale= 12.5 m
  7. 7One Kilometre On The Map= 4.00 cm

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why count gaps rather than lines?

Because five fence posts have four gaps. Counting lines instead of intervals is the classic off-by-one error in contour reading.

What does close contour spacing mean?

Steep ground. The horizontal distance between lines is the run for a fixed rise, so tightly packed contours are cliffs.

Related Calculators

Contour Interval Calculator – Calculate Contour Interval