ToolsEnvironmentalContamination Assessment

pH Calculator

Calculate pH from H⁺ concentration or vice versa. Includes soil/water classification and concrete aggressivity assessment per BRE SD1 / BS 8500.

Last updated 14 April 2026

About this tool

Calculate pH from hydrogen ion concentration or convert a pH value to [H⁺] and [OH⁻] concentrations. The tool classifies the result on the acidic-alkaline scale and — uniquely for a pH calculator — assesses concrete aggressivity per BRE Special Digest 1 / BS 8500.

This makes it directly useful for contaminated land and geotechnical assessments where you need to know both the chemistry and the practical implications for buried concrete design.

Results are colour-coded from red (strongly acidic) through neutral to violet (strongly alkaline), giving an instant visual indication of where the sample sits on the scale.

How to use this tool

1. Choose input method — enter a pH value directly, or enter the H⁺ concentration in mol/L.

2. Enter the value — pH range is 0-14. For H⁺ concentration, use scientific notation (e.g. 0.001 for 10⁻³).

3. Review all outputs — pH, [H⁺], [OH⁻], classification, and concrete design class are all calculated simultaneously.

Technical information

pH = -log₁₀([H⁺])

[OH⁻] = Kw / [H⁺], where Kw = 10⁻¹⁴ at 25°C

Concrete aggressivity classes are based on BRE Special Digest 1 (SD1) and BS 8500-1. The design chemical class (DC-1 to DC-4) determines the concrete specification required for buried elements. pH < 4.5 is the most aggressive condition (DC-4), requiring specialist design. DC-3 covers pH 4.5–5.5, DC-2 covers pH 5.5–6.5, and DC-1 (least aggressive) applies at pH ≥ 6.5.

Limitations

The Kw = 10⁻¹⁴ value is for 25°C. At other temperatures, Kw varies (e.g. 10⁻¹⁴·¹⁷ at 20°C). For most environmental assessments this is negligible.

Concrete aggressivity depends on more than pH alone — sulfate concentration, magnesium content, and mobility of groundwater are also critical factors per BRE SD1. pH is just one input to the full ACEC classification.

The DC class boundaries shown are simplified from BRE SD1 Table 2 (pH < 4.5 = DC-4, 4.5–5.5 = DC-3, 5.5–6.5 = DC-2, ≥ 6.5 = DC-1). The full ACEC assessment requires consideration of sulfate concentration, brownfield vs greenfield, natural ground vs made ground, and static vs mobile water conditions.

Revision history

14 April 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.

Input method

pH value

Range: 0 (strongly acidic) to 14 (strongly alkaline)

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