Level Difference Calculator
Calculate the signed and absolute elevation difference between two points, or derive Point B RL from a benchmark RL and staff readings from one instrument setup.
Convention: ΔRL = RL(B) − RL(A). A positive result means a rise from A to B; a negative result means a fall.
How to use this calculator
Quick example: Point A RL 100.000 and Point B RL 101.250 gives a rise of 1.250.
1. Enter level data
Enables gradient, slope percentage and slope angle.
2. Results
Enter the required level data.
Export results
Calculation method
Direct method: ΔRL = RL(B) − RL(A). Staff method: HI = RL(A) + BS, then RL(B) = HI − IS/FS. If horizontal distance is supplied, slope % = ΔRL ÷ distance × 100 and slope angle = atan(ΔRL ÷ distance).
Frequently asked questions
What does a positive level difference mean?
Point B is higher than Point A by the reported amount.
What does a negative result mean?
Point B is lower than Point A, so the movement from A to B is a fall.
How is Point B RL calculated from staff readings?
Add the backsight to the known Point A RL to obtain HI, then subtract the Point B IS or FS reading.
How is gradient calculated?
The signed level difference is divided by horizontal distance. The calculator also reports percentage and angle.
Can I use feet?
Yes. Use the same unit for RLs, staff readings and horizontal distance.
Explore more calculators on the Site Survey tools page.