Standard grading tolerances: pavement subgrade — ±0.05 ft (most DOTs); building pad finish grade — ±0.10 ft; rough grading — ±0.10 to ±0.20 ft; concrete flatwork subgrade — ±1/4 inch (±0.021 ft) per ACI 117; athletic field — ±0.05 ft. Always confirm with the project specification — requirements vary by jurisdiction and project type.
What a Grading Tolerance Means
A grading tolerance is the maximum allowable deviation from design elevation — either direction. A tolerance of ±0.10 ft means within 0.10 ft high AND within 0.10 ft low. Consistently low surface, even within tolerance, may cause drainage problems. Consistently high requires more expensive base course. The tolerance is a band you stay within, not a target you aim for on the low side.
Tolerances by Work Type
| Work Type | Typical Tolerance | Reference |
|---|---|---|
| Mass grading / rough grade | ±0.20 ft | Project spec |
| Road embankment slope | ±0.10 ft | State DOT |
| Pavement subgrade | ±0.05 ft | Most state DOTs |
| Building pad finish grade | ±0.10 ft | Geotech report |
| Concrete flatwork subgrade | ±1/4 in (±0.021 ft) | ACI 117 |
| Athletic field finish grade | ±0.05 ft | Sports turf spec |
| FAA airport runway | ±0.01 ft | FAA AC 150/5370 |
| Detention basin outlet invert | ±0.05 ft | Civil drawings |
How to Measure Grading Tolerance in the Field
Spot Elevations
Set up the level, calculate HI, and check elevations at a grid across the finished surface. Compare each spot to design. Flag out-of-tolerance points for re-grading before paving or final inspection. Typical grid: 25 ft for finish grade, 50 ft for rough grade.
10-Foot Straightedge (Concrete Subgrade)
ACI 117 and most DOT specs require a 10-ft rigid straightedge check on concrete subgrade. Place the straightedge in multiple directions; maximum gap between straightedge and surface must not exceed 1/4 inch. This catches local humps and hollows that 25-ft spot elevation grids miss.
When Tolerance Is Exceeded
- Over grade (high): Scarify and blade back to design, re-compact. For concrete subgrade, re-grade before the concrete crew sets up.
- Under grade (low): Add material in a properly thick lift, compact to spec, re-verify. Document failure, corrective action, and passing re-test in Gradelog — all three must appear in the as-built package.
Practical Tips
- Grade to the tight (center) side of tolerance — easier to remove a bit than add back after fine grading.
- Check final grade the morning after, not right after grading — traffic settles freshly graded surfaces.
- Re-verify HI every 2–3 hours — a 0.05-ft HI shift makes every grade check after it 0.05 ft wrong.
- Flag out-of-tolerance spots immediately with paint flags — much harder to relocate later.