pH Calculator
Estimate pH from the concentration of a strong acid or base using a 25°C ideal-solution approximation.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
pH
Dots show recalculated samples. Other inputs stay fixed.
About this calculator
This simplified estimate assumes a fully dissociated strong acid or base, ideal behavior, and 25°C (pKw = 14). It does not model weak-acid equilibria, activity effects, mixtures, or concentrated solutions.
Worked example
calculated with the default values below
Concentration 0.01 M · Substance type Strong acid (HA) pH 2.00 · pOH 12.00 · Hydrogen ion concentration 0.010000 M · Hydroxide ion concentration 0.000000 M · Solution Strongly acidic · Ion product of water 1.000e-14
Data sources
Disclaimer
These calculators give general conversion results. Rounding and the precision of the value you enter both affect the output, so treat displayed decimals as indicative rather than exact.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
pH = −log10(H); H = {c, m = 0; Kw ÷ c, m = 1}; Kw = 10^(−(14 − 0.02·(T − 25)))
- pH
- pH value
- H
- Equivalent human age (years)
- c
- Entered concentration (M)
- Kw
- Water ion product
- T
- Temperature (°C)
- m
- Substance code: 0 acid, 1 base
m = 0 for acid, m = 1 for base. pOH = 14 − pH, [OH⁻] = Kw ÷ H; c floor 1e-10 M; type thresholds pH 3/6.5/7.5/11.
Frequently asked questions
Why does raising the temperature shift the neutral pH point?
The tool computes the ion product of water as 10 to the power of -(14 - 0.02*(temperature - 25)), so at 25°C neutral is 7 but at 50°C the neutral pH falls to about 6.5 because Kw grows with heat. A 0.01 M strong acid still reports pH 2 regardless, but a base's hydrogen ion value changes with temperature since h equals Kw divided by concentration. The 'neutral' label therefore tracks temperature instead of always reading 7.