Linear interpolation
The calculator assumes one constant straight gradient between the two known points. Each intermediate level is calculated in direct proportion to its distance from the start chainage.
Worked level schedule example
From chainage 0.000 at level 100.000 m to chainage 20.000 at level 99.500 m, the total fall is 0.500 m over 20.000 m. At 5 m intervals the calculated levels are 100.000, 99.875, 99.750, 99.625 and 99.500 m at chainages 0, 5, 10, 15 and 20 respectively.
That straight grade is a 2.5% fall, equivalent to 25 mm per metre or 1 in 40. The schedule interpolates only between the supplied endpoints; it does not decide whether that gradient is suitable.
Exact end point
If the chosen interval does not divide the total length exactly, the schedule still includes a final row at the precise end chainage rather than overshooting or omitting it.
Suitable uses
For common 1:n values and quick fall checks, use the printable gradient and fall tables.
For a sequence of connected drainage runs with coordinates and invert levels, use the Manhole Schedule Gradient Checker.
The schedule is useful for formation levels, kerb lines, drainage inverts and simple grading checks where a single constant gradient is intended. It is not a vertical-curve calculator.
Frequently asked questions
Can the end level be higher than the start level?
Yes. The schedule will show a rising gradient and interpolate levels accordingly.
Does this support vertical curves?
No. It assumes a straight grade between the endpoints. Parabolic vertical curves require curve length and grade data.
Why is the final interval shorter?
The calculator always includes the exact end chainage. When the total length is not an exact multiple of the interval, the final segment is shorter.