Tape Sag Correction Calculator

Application: Exploration and Geology

  • Format: Online Tool Tool Tip
  • Fee for Use: Free Tool Tip
  • Enrollment: Not Required Tool Tip


An interactive tool for determination of catenary sag correction and true length for tape measurements; available for metric and imperial units.

Notes on Tape Sag Correction 'Catenary' Calculator (metric)

  • Select the required output, then set the other parameters to the required values.
  • This tool works with metric units; for an imperial units version click the "Imperial Units" button.

For a more complete definition of Catenary and the formula, see below.

Explain Sag

Sag Correction:

When a tape is suspended from each end, it forms a curve called a catenary .  Because the curve is longer than the straight-line distance between the ends of the tape, the tape always reads longer than the actual distance.  The correction is therefore a negative quantity.

If the weight of the tape is w kilograms per meter, kg/m (or pounds per foot, lb/ft) , the unsupported length of tape is l meters (or feet), P is the tension applied to the tape in kilograms (or pounds), then the sag correction, Cs , will be

Sag Formula

Consistent units, metric or imperial must be used throughout.

'corrected' value = measured value - correction

Tool Parameters

Values displayed with a may be changed ... click on a value to display an entry form ... or use the arrows right of a value to select from a list.

Tool Behaviour

This tool exhibits spreadsheet-like behaviour ... change a value and related values are re-calculated automatically.

SVG Plugin

This tool needs SVG viewing capabilities. If your browser does not support SVG then download the Adobe plugin here.

Download Adobe SVG here