Vertical Curve Calculator
Calculate an equal-tangent parabolic crest or sag curve from PVI chainage and tangent RL, entering and departing grades, horizontal length and a BVC-based interval. The result shows signed grade change, K value, the curve high or low point, and a printable chainage/RL table.
Uses only this tool title and its public link. Inputs, results, coordinates and filenames are not included. Sharing starts only when you press the button.
Free advisory field tool — every result is computed in your browser from the inputs you provide and is advisory and unverified, not for survey deliverables. Where a published guideline applies, results only ever read “within guideline” or “exceeds guideline — review”. The full working is shown for every calculation so each step can be re-checked. Registered surveyor confirmation required before reliance.
K value, turning point and RL table
One symmetric crest curve was calculated from the supplied tangent grades and horizontal length.
- Curve type
- crest
- Signed grade change g2 - g1 (%)
- -3
- K value (m / %)
- 100
- BVC chainage (m)
- 1050
- BVC RL (m)
- 99
- PVI chainage (m)
- 1200
- PVI tangent RL (m)
- 102
- Curve RL at PVI chainage (m)
- 100.875
- EVC chainage (m)
- 1350
- EVC RL (m)
- 100.5
- high point chainage (m)
- 1250INTERIOR
- high point RL (m)
- 101
| Point | Chainage (m) | x from BVC (m) | RL (m) | Grade (%) |
|---|---|---|---|---|
| BVC | 1050 | 0 | 99 | 2 |
| Interval 1 | 1100 | 50 | 99.875 | 1.5 |
| Interval 2 | 1150 | 100 | 100.5 | 1 |
| Interval 3 | 1200 | 150 | 100.875 | 0.5 |
| Interval 4 | 1250 | 200 | 101 | 0 |
| Interval 5 | 1300 | 250 | 100.875 | -0.5 |
| EVC | 1350 | 300 | 100.5 | -1 |
Show the working
- signed grade change Ag2 - g1 (percentage points)-3
- absolute grade change |A|abs(g2 - g1)3
- K valueL / |A| (m / %)100
- BVC chainagePVI chainage - L / 21050
- BVC RLPVI tangent RL - (g1 / 100) * (L / 2)99
- EVC chainagePVI chainage + L / 21350
- EVC RLPVI tangent RL + (g2 / 100) * (L / 2)100.5
- curve RL at PVI chainageRL_BVC + (g1 / 100)x + A*x^2 / (200L), x = L / 2100.875
- zero-grade offset-g1*L / A; null when outside 0 <= x <= L200
- reported high/low offsetzero-grade point within curve; otherwise endpoint RL extremum200
- table row countBVC + interval stations + EVC7
Working trace rendered from the same computation as the result above — re-check any step by hand before relying on it.
How to use the vertical curve calculator
Enter the PVI, tangent grades, horizontal curve length and schedule interval, then review the parabolic curve outputs.
Enter the PVI data
Supply the PVI chainage and tangent RL together with the entering and departing grades as signed percentages.
Set length and interval
Enter the horizontal equal-tangent curve length and the BVC-based interval for the displayed RL schedule.
Review and print the schedule
Inspect the K value, BVC, EVC, curve turning point, interval RL rows and calculation trace before printing the table.
Questions about Vertical curve calculator
What does a vertical curve calculator in Australia calculate?
This vertical curve calculator calculates an equal-tangent parabolic crest or sag curve, K value, turning point and chainage-RL schedule for review in Australia.
How are positive and negative grades interpreted?
A positive percentage rises with increasing chainage and a negative percentage falls. The horizontal curve length is centred on the entered PVI chainage.
Does the schedule choose a design criterion?
No. It evaluates the entered curve geometry and does not select sight-distance criteria, road authority requirements, datum or construction acceptance values.
Safety & scope
SurveyMarkup helps prepare and review working information. Every professional decision remains with the registered surveyor, and original data and final outputs require qualified review.
Assistance only - professional review remains required.