ToolsFabric SurveyConcrete Testing

Rebound Hammer Processor

Free online Schmidt hammer processor. Calculates estimated compressive strength with outlier rejection per BS EN 12504-2 and BS EN 13791.

Last updated 17 March 2026

About this tool

Process Schmidt rebound hammer test results in accordance with BS EN 12504-2. The tool handles outlier rejection, orientation and surface corrections, and provides an indicative strength estimate.

Designed for site engineers and technicians carrying out non-destructive concrete testing as part of condition assessments or quality verification.

How to use this tool

Enter rebound numbers — at least 10 comma-separated readings from the test area.
Select orientation — the angle at which the hammer was used (horizontal, upward, downward, or 45°).
Select surface type — formed or trowelled. Trowelled surfaces receive a correction of −2.
Review results — the tool filters outliers, reports the corrected rebound number, an indicative cube strength, and a consistency assessment.

Technical information

Outlier rejection — per BS EN 12504-2, readings differing from the median by more than 6 units are rejected. If more than 20% of readings are rejected, the entire test is discarded.

Result — the median of valid readings, not the mean.

Orientation corrections — corrections vary with rebound number (Type N hammer). At higher rebound numbers, the gravitational effect is proportionally smaller and corrections decrease. Values are interpolated from the manufacturer's published table.

Strength estimate — a generic linear correlation is used for indicative purposes only. Rebound number correlations are not a substitute for core testing.

Limitations

Rebound number is affected by surface moisture, carbonation, aggregate type, and member thickness.
The strength estimate is indicative only — site-specific calibration curves should be used where available.
Orientation corrections are for the Original Schmidt Type N hammer. Other hammer types may require different corrections.

Revision history

17 March 2026: Initial release

Disclaimer

This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.

Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.

All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.

By using this tool, you accept full responsibility for how you interpret and apply the information provided.

Spotted an error? Let us know.

Rebound numbers (comma-separated, min. 10)

Orientation angle

Surface type