Work out manhole spacing instantly with clear inputs, formula shown and shareable results.
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.
Manhole count
Manholes = ceil(length / maximum spacing) + 1 + bends + junctions
Preliminary estimate only. Manhole spacing, chamber sizes and access requirements must follow the drainage code and authority standards.
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.
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.
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.