Leveling Calculator — Differential Leveling
Compute sequential elevations from backsight and foresight readings, with instrument heights, arithmetic sums and an optional known-end closure check.
Reduce a sequence of differential-leveling observations to elevations. Each row represents one instrument setup with a backsight on the current known point and a foresight on the next turning point or endpoint. The calculator reports instrument elevations and the accumulated rise or fall, with an optional check against known endpoint control.
How to use this tool
- Enter the elevation of the starting benchmark in the chosen datum.
- Enter one backsight and one foresight for each successive instrument setup.
- Select metres or international feet for every reading and elevation.
- Optionally enter a known endpoint elevation, then inspect the computed misclosure and setup table.
Formula
HI = current elevation + BS; next elevation = HI − FS; total change = ΣBS − ΣFS
BS and FS are nonnegative staff readings for an upright staff. HI is the elevation of the instrument’s horizontal line of sight, not its height above the ground. Every foresight endpoint becomes the next setup’s backsight point.
Example
Starting at 100.00 m, the first readings BS = 1.89 m and FS = 0.72 m give HI = 101.89 m and next elevation 101.17 m. A second setup with BS = 1.96 m, FS = 0.87 m gives final elevation 102.26 m, a total rise of 2.26 m.
Frequently asked questions
Can I enter several intermediate sights from one setup?
Not as separate rows. This layout represents a sequence of turning-point transfers. Treating intermediate sights as new setups would repeatedly change the reference point and produce incorrect elevations.
What does positive endpoint misclosure mean?
Computed endpoint elevation is higher than the known control elevation. The reported sign is computed minus known. No acceptance tolerance or adjustment distribution is applied.
Can elevations be negative?
Yes. Elevation is relative to your selected datum, so negative values can be valid. Staff readings here must be nonnegative; inverted-staff conventions need a different input model.
What observation corrections are included?
None. Curvature, refraction, collimation, staff calibration and field procedures must be addressed separately. The arithmetic does not prove survey accuracy. Up to 100 setups and 20,000 text characters are accepted, and all readings must share a unit and datum.
Sources
Last updated: 2026-10-30