pH / Acid–Base Calculator

pH = −log₁₀[H⁺], pOH = −log₁₀[OH⁻], pH + pOH = 14.00 (25 °C)

Convert between pH, pOH, hydrogen-ion and hydroxide concentration, and get the pH of a strong acid or base.

Inputs

Mode

Known quantity

Dimensionless logarithmic value.

Result

pH = 7

pOH = 7, [H⁺] = 1 × 10⁻⁷ mol/L, [OH⁻] = 1 × 10⁻⁷ mol/L

Calculation

Entered pH
7
pH
pH = −log₁₀[H⁺]
[H⁺] = 1 × 10⁻⁷ mol/L
pH = 7
pOH
pOH = pKw − pH (pKw = 14.00 at 25 °C)
pOH = 7
Hydroxide concentration
[OH⁻] = 10^(−pOH)
[OH⁻] = 1 × 10⁻⁷ mol/L

Inputs

Mode: Direct conversion
Entered value: 7
pKw used: 14.00 (25 °C, conventional)

pKw = 14.00 is the conventional value for pure water at 25 °C. Kw is temperature dependent (for example ≈ 13.99 at 24 °C and ≈ 13.26 at 50 °C), so the pH ↔ pOH relationship shifts away from 25 °C.

Concentrations are treated as ideal: activities and ionic-strength effects are not included, so measured pH can differ from the calculated value.

No compound identity, dissociation behaviour or concentration is assumed — every value comes from your input.

Where this sits on the scale

024678101214

pH 7.00 neutral at 25 °C

About this calculator

pH and pOH are logarithmic measures of the hydrogen-ion and hydroxide-ion activity of an aqueous solution. Entering any one of pH, pOH, [H⁺] or [OH⁻] fixes the other three through the ion product of water.

The conventional value pKw = 14.00 applies to water at 25 °C. Kw is temperature dependent — at 37 °C neutral water has a pH near 6.8 — so results from this calculator are stated for 25 °C and are not silently temperature corrected.

The strong acid / strong base mode assumes complete dissociation of a monoprotic species, so [H⁺] equals the analytical concentration. Weak acids and bases need their Ka or Kb, and polyprotic acids need each dissociation step; neither is assumed here. Very dilute solutions (below about 10⁻⁶ mol/L) also need the water autoprotolysis term, which this simple treatment omits.

LabReadyTools is provided as a calculation aid. Users remain responsible for verifying calculations, units, chemical compatibility, experimental procedures and applicable safety requirements before laboratory use.