FREE FIELD CALCULATOR
Grade check calculator
Read a benchmark and a point, then find the point elevation and how much cut or fill reaches your target.
What you’ll need
- A known benchmark elevation
- A backsight on the benchmark and a foresight on your point
- The target elevation and job tolerance, for a cut/fill check
- Every reading in decimal feet
Enter the readings above.
The result shows the point elevation and, if you supply a target, the difference from it.
Try it with these numbers
- Enter benchmark 100.00 and backsight 5.25. These establish a height of instrument (HI) of 105.25 ft.
- Enter foresight 4.75, target 100.25 and tolerance 0.05.
- Choose Calculate grade. The point elevation should be 100.50 ft, with CUT 0.25 ft—three inches high.
- Check the direction against what you see. A larger foresight reading puts the point lower. Recheck the setup if the result doesn’t fit the ground.
Reading your result
Point elevation is the height of the point on your benchmark’s reference. HI is the elevation of the instrument’s line of sight, not the tripod height.
CUT means the point is above the target; FILL means it is below. PASS means within the tolerance you entered, not acceptance under a contract or standard.
Hundredths of a foot on a tape
Rods read in tenths and hundredths of a foot; tapes read in inches. Each value is rounded to the nearest 1/16 inch. Results above show both.
| Decimal feet | On a tape |
|---|---|
| 0.01 ft | 1/8" |
| 0.02 ft | 1/4" |
| 0.03 ft | 3/8" |
| 0.04 ft | 1/2" |
| 0.05 ft | 5/8" |
| 0.06 ft | 3/4" |
| 0.07 ft | 13/16" |
| 0.08 ft | 15/16" |
| 0.09 ft | 1 1/16" |
| 0.10 ft | 1 3/16" |
| 0.25 ft | 3" |
| 0.50 ft | 6" |
| 0.75 ft | 9" |
Where this goes wrong on site
- Swapping the backsight and foresight. The backsight adds to the benchmark; the foresight subtracts from HI.
- Reading feet-and-inches as decimal feet. A tenth of a foot is 1.2 inches, not 1 inch.
- Rod not straight up. Have the rod rocked slowly toward and away from the instrument and take the lowest reading, or use a rod level.
- A turning point that moves. Put turning points on something firm whose elevation won’t change while the instrument moves, not soft ground or a loose stone.
- Bumping the tripod. Leaning on the instrument or stepping near its legs can knock it off level. Check the bubble often; if it moved, rerun the readings.
- Never closing the loop. Run your levels back to the starting benchmark or another proven point, so a mistake shows up before the stakes go in. Keep backsight and foresight distances about equal, and check the level with a two-peg test using stakes 200 to 300 feet apart.
Sources: USDA NRCS Engineering Field Handbook, Part 650, Chapter 1: Surveying
How the math works
HI = benchmark elevation + backsight. Point elevation = HI − foresight. Difference = point elevation − target. Positive means cut; negative means fill. For a turning point, establish its elevation before moving the instrument, then take a fresh backsight on that same point. The private running field book keeps multiple points, notes and setup history.
Keep the number with the job
Calculate above, then download a Letter or A4 PDF, copy the result or share it from your phone. The result sheet keeps your inputs and assumptions. Changing an input means you need to calculate again before exporting.
Open the private field workspace for saved jobs and reports across your phone and computer, or read the free-calculator guide. Tell Jesse what would make this easier on your job.
Useful on your job?
Share this free calculator with someone who could use it, or tell Jesse what needs improving.
Shares the tool link only, without your measurements. https://driftlesssolutions.us/tools/grade-check/