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Survey Levelling Calculator

Work out survey levelling instantly with clear inputs, formula shown and shareable results.

About Survey Levelling Calculator

The height of collimation method adds the backsight staff reading to the known benchmark level to get the instrument's line of sight, then subtracts each foresight to obtain the reduced level of that point. A larger foresight than backsight means the ground has fallen, because the staff had to be read further down.

Formulas

Height of collimation

HI = benchmark RL + backsight reading

Reduced level

RL = HI - foresight reading

Worked example

With the default values below, Survey Levelling Calculator returns Reduced level of the new point of 98.8250. Change any input above and every figure here is recalculated in your browser.

Inputs used

Benchmark reduced levelminimum -1,000 m
100 m
Backsight reading on benchmarkminimum 0 m
1.235 m
Foresight reading at new pointminimum 0 m
2.41 m

Results

Reduced level of the new point
98.8250 m
Height of collimation
101.2350 m
Difference in level
-1.1750 m
Rise or fall
Fall of 1.175 m

Step by step

  1. 1Values used
  2. 2Height of collimation
  3. 3Reduced level
  4. 4Reduced level of the new point= 98.8250 m
  5. 5Height of collimation= 101.2350 m
  6. 6Difference in level= -1.1750 m
  7. 7Rise or fall= Fall of 1.175 m

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, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 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

How is the Survey Levelling figure worked out?

HI = benchmark RL + backsight reading. The height of collimation method adds the backsight staff reading to the known benchmark level to get the instrument's line of sight, then subtracts each foresight to obtain the reduced level of that point.

Which method is better, collimation or rise and fall?

Rise and fall provides an arithmetic check on every intermediate sight and is preferred where accuracy matters. Height of collimation is faster when there are many intermediate points from one setup.

What values do I need to enter?

This calculator takes 3 inputs: Benchmark reduced level, Backsight reading on benchmark, Foresight reading at new point. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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