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Manhole Spacing Calculator

Work out manhole spacing instantly with clear inputs, formula shown and shareable results.

About Manhole Spacing Calculator

Manholes are needed at both ends of every straight run, so the count is the number of spans plus one, with additional chambers at every change of direction, gradient or pipe size and at each junction. Maximum spacing is set by rodding and jetting reach, commonly 30 to 45 metres depending on pipe size.

Formula

Manhole count

Manholes = ceil(length / maximum spacing) + 1 + bends + junctions

Worked example

With the default values below, Manhole Spacing Calculator returns Manholes required of 20. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sewer lengthminimum 0.1 m
400 m
Maximum permitted spacingminimum 1 m
30 m
Changes of directionminimum 0
3
Junctionsminimum 0
2

Results

Manholes required
20
Straight spans
14
Actual spacing achieved
28.57 m
Spacing check
Within the permitted spacing

Step by step

  1. 1Values used
  2. 2Manhole count
  3. 3Manholes required= 20
  4. 4Straight spans= 14
  5. 5Actual spacing achieved= 28.57 m
  6. 6Spacing check= Within the permitted spacing

Assumptions and limits

  • The result is derived only from the 4 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 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Manhole spacing, chamber sizes and access requirements must follow the drainage code and authority standards.

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

Preliminary estimate only. Manhole spacing, chamber sizes and access requirements must follow the drainage code and authority standards.

Frequently Asked Questions

How is the Manhole Spacing figure worked out?

Manholes = ceil(length / maximum spacing) + 1 + bends + junctions. Manholes are needed at both ends of every straight run, so the count is the number of spans plus one, with additional chambers at every change of direction, gradient or pipe size and at each junction.

Can bends be made without a manhole?

Small deflections in flexible pipe are allowed, but a true change of direction needs access because a rod or jet cannot negotiate the bend. Blind bends are the most common cause of an unclearable blockage.

What values do I need to enter?

This calculator takes 4 inputs: Sewer length, Maximum permitted spacing, Changes of direction, Junctions. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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