Tip: Add your survey points, set tolerances, then press Calculate.
Exports become available after a calculation.
Calculator inputs
Responsive form: three columns on large screens, two on tablets, one on phones.
Formula used
Elevations are converted to millimeters for consistent calculations.
Deviation vs reference
Reference elevation R is either:
• Average: R = (Σ zᵢ) / n
• Target: R = ztarget
Point deviation: dᵢ = zᵢ − R
Max absolute deviation: max |dᵢ|
• Average: R = (Σ zᵢ) / n
• Target: R = ztarget
Point deviation: dᵢ = zᵢ − R
Max absolute deviation: max |dᵢ|
Best-fit plane (least squares)
Plane model: z = a·x + b·y + c
Residual: rᵢ = zᵢ − (a·xᵢ + b·yᵢ + c)
Slope magnitude: S = √(a² + b²) (mm/m)
Flatness (P-V): max(rᵢ) − min(rᵢ)
Residual: rᵢ = zᵢ − (a·xᵢ + b·yᵢ + c)
Slope magnitude: S = √(a² + b²) (mm/m)
Flatness (P-V): max(rᵢ) − min(rᵢ)
Needs at least 3 non-collinear points.
Pass / fail logic
- Absolute deviation passes if max |dᵢ| ≤ allowable.
- Slope passes if S ≤ allowable.
- Flatness passes if P-V ≤ allowable.
How to use this calculator
- Choose your elevation input unit and reference mode.
- If using Target mode, enter the design elevation.
- Set tolerances for deviation, slope, and flatness.
- Enter points with X, Y (meters) and elevation.
- Press Calculate to see the results.
- Download CSV or PDF for inspection documentation.
Field tip: Capture corners and mid-span points to detect tilt and local highs.
Example data table
Example: six readings across a 12 m × 6 m foundation. Use the “Fill example” button to load these values.
| Point | X (m) | Y (m) | Elevation (mm) | Typical note |
|---|---|---|---|---|
| P1 | 0 | 0 | 1000 | Baseline corner. |
| P2 | 6 | 0 | 1002 | Rise along X. |
| P3 | 12 | 0 | 1001 | Small dip. |
| P4 | 0 | 6 | 1000 | Edge repeat. |
| P5 | 6 | 6 | 1003 | Local peak. |
| P6 | 12 | 6 | 1002 | Edge rise. |
You can add unlimited points for larger foundations.