🧫 pH Calculator
Enter a pH, pOH, [H⁺], [OH⁻], or a strong-acid/strong-base concentration and get all four values at 25 °C, plus whether the solution is acidic, neutral, or basic.
🧫 Result
Neutral
Assumes 25 °C (Kw = 1×10⁻¹⁴, pH + pOH = 14) and full dissociation of strong acids/bases. Weak acids and bases need their Ka/Kb. For educational use — verify against authoritative sources and follow proper lab safety.
Four numbers, one equilibrium
pH, pOH, [H⁺] and [OH⁻] are four windows onto the same water equilibrium. Fix any one at 25 °C and the others are determined by pH + pOH = 14 and [H⁺][OH⁻] = 10⁻¹⁴. Seeing all four together makes it clear why a strong base with tiny [H⁺] still has a well-defined, high pH.
Prepare the acid or base with the Molarity Calculator, step a stock down with the Dilution Calculator, and come back here to read off the resulting pH.
❓ Frequently Asked Questions
How is pH defined?
pH is the negative base-10 logarithm of the hydrogen-ion concentration: pH = −log₁₀[H⁺], with [H⁺] in mol/L. Equivalently, [H⁺] = 10^(−pH). Lower pH means more H⁺ and a more acidic solution; each whole pH unit is a tenfold change in [H⁺].
How are pH, pOH, [H⁺] and [OH⁻] related?
At 25 °C water's ion product is Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴, so pH + pOH = 14. From any one of the four you can get the others: [OH⁻] = Kw ÷ [H⁺], pOH = −log₁₀[OH⁻], and pH = 14 − pOH. The calculator does all of these conversions at once.
How do I get pH from a strong acid or base concentration?
A strong monoprotic acid like HCl dissociates completely, so [H⁺] equals its molar concentration and pH = −log₁₀(concentration): 0.01 M HCl gives pH 2. A strong monobasic base like NaOH sets [OH⁻] equal to its concentration, so pOH = −log₁₀(concentration) and pH = 14 − pOH: 0.001 M NaOH gives pOH 3 and pH 11.
Does this work for weak acids and bases?
Not directly. Weak acids and bases only partially ionise, so their pH depends on the acid/base dissociation constant (Ka or Kb) and requires an equilibrium calculation (often the Henderson–Hasselbalch equation for buffers). The strong-acid/strong-base modes here assume complete dissociation and should not be used for weak species or very dilute solutions where water's own ionisation matters.
Why 25 °C?
Kw changes with temperature, so neutral pH is only exactly 7 at 25 °C; at higher temperatures neutral pH is lower. This tool assumes 25 °C (Kw = 1 × 10⁻¹⁴). For educational use — verify against authoritative sources and follow proper lab safety when handling acids and bases.