Elevation Difference Calculator
Subtract two hub, invert, or finish-grade elevations. The result is the signed difference (positive means the second point is higher) plus the absolute cut/fill in feet and inches.
Enter your values, then press Calculate.
How to calculate
Enter elevation A (start, existing, or invert) and elevation B (end, finish, or hub). Use the same datum for both. The calculator reports how much B is above A, and the absolute difference for cut/fill.
Formula
Difference (ft) = elevation B − elevation A. Absolute difference is |B − A|. Inches = absolute difference × 12.
Common use cases
- Hub-to-hub shots
- Invert to finish-grade checks
- Cut/fill between two plan elevations
- Converting a decimal-foot shot to inches
Assumptions
- Both elevations are on one datum (same benchmark, same units before subtraction).
- Difference = elevation B − elevation A. Positive means B is higher than A.
- Inches convert to feet before subtracting.
- A zero difference is a level pair, not an error.
Limitations
- Does not convert assumed elevations to a published datum.
- Does not apply a level-loop closure or instrument HI.
- Does not turn a cut into cubic yards. Pair with a length and width elsewhere.
- Does not station the points. Use station difference for the horizontal run.
Worked examples
102.50 minus 100.00 is 2.50 ft
Proposed 102.50 minus existing 100.00 is 2.50 ft of fill at that spot. Swap the two numbers and the sign flips to cut.
1. B minus A
102.5 − 100 = 2.5 ft
2. Absolute difference in inches
2.5 ft × 12 = 30 in
Cut when B is lower
1. B minus A
9 − 12 = -3 ft
2. Absolute difference in inches
3 ft × 12 = 36 in
Cut and fill from the sign
The primary result is B minus A, not an absolute. If A is existing ground and B is proposed grade, a positive difference is fill and a negative difference is cut. 102.50 − 100.00 = +2.50 ft (fill). 9.00 − 12.00 = −3.00 ft (cut). The absolute row is the same number without the sign, plus that magnitude in inches, for field notes that only record “cut 3.00 ft.”
Existing vs proposed, hub vs invert
Label A and B the same way the plans do. Common pairs: existing vs proposed pad, hub vs finish, invert in vs invert out. The calculator does not know which point is “ground.” If you reverse the pair, the sign flips and the cut/fill story reverses. For pipe grade, take the two invert elevations and the station run, then open pipe slope rather than this page alone.
Field-grade example
A pad is called at 88.40. The existing shot at the same hub is 86.75. Enter 86.75 as A and 88.40 as B: +1.65 ft, which is 19.8 in of fill. If the rod is in inches, convert each elevation first or use the inch unit on that input. Do not mix a decimal-foot finish with a tenth-of-an-inch architect tape without converting both to the same unit.
Which point is A and which is B
If A is existing grade 100.00 and B is proposed pavement 102.50, the difference is +2.50 ft of fill at that point. Reverse the labels and you get a cut of the same magnitude. The sign is only useful if you keep A and B consistent with the plans (existing vs proposed, hub vs invert, top of curb vs flowline). For a pipe, take invert to invert and then open pipe slope with the station run.
Related calculators
- Percent Grade CalculatorConvert rise and run into percent grade, slope ratio, and feet per 100 feet.
- Station Difference CalculatorFind the distance between two stations in the 100-foot stationing system.
- Pipe Slope CalculatorConvert elevation drop and run into percent grade, ratio, and inches per foot.
FAQ
Why is the difference negative?
Negative means elevation B is below A. If A is existing grade and B is proposed, a negative result is cut. Use the absolute difference when you only need magnitude.
Is positive fill or cut?
Positive B minus A means B is higher. Existing-to-proposed: positive is fill, negative is cut. Invert-to-invert along a pipe: positive means the second invert is higher (adverse to typical drainage unless you swapped the points).
Can I mix feet and inches?
Yes. Each elevation has its own unit. Both are converted to feet before subtracting.
Do I need the same datum?
Yes. Both shots must be on the same vertical datum (project, NAVD88, or a job hub). Mixing a finish-floor elevation with an unadjusted GPS ellipsoid height is not a cut/fill.
Can I enter rod readings instead of elevations?
Only after you convert them to elevations with the HI. This page subtracts two elevations. A rod reading without an HI is not an elevation.
Disclaimer
These calculators are estimating tools for planning and field checks. They are not a substitute for approved plans, specifications, licensed professional engineering, or governing standards. Confirm densities, waste factors, and yields with your supplier and project documents.