pH Calculator
Part of Chemistry Calculators
Calculate pH, pOH, hydrogen ion concentration [H+], and hydroxide ion concentration [OH-] with instant conversions.
How to Use the pH Calculator
- Select calculation type: Choose whether you're starting with H+ concentration, OH- concentration, pH, or pOH.
- Enter the value: Input your known value. For concentrations, select the appropriate unit (M, mM, μM, or nM).
- Calculate: Click the calculate button to instantly compute all related values.
- View results: The calculator displays pH, pOH, [H+], and [OH-] with a visual pH scale indicator showing acidity or basicity.
Understanding pH and pOH
pH is a logarithmic scale that measures the acidity or basicity of aqueous solutions. The pH scale ranges from 0 to 14, where pH 7 is neutral (pure water at 25°C), values below 7 indicate acidic solutions, and values above 7 indicate basic (alkaline) solutions. Each unit change in pH represents a tenfold change in hydrogen ion concentration. Use our Molarity Calculator to determine acid or base concentrations in your solutions.
The relationship between pH and hydrogen ion concentration is defined by the equation: pH = -log[H+]. Similarly, pOH measures the hydroxide ion concentration using pOH = -log[OH-]. At 25°C, pH and pOH are related by the equation: pH + pOH = 14.
Key pH Formulas
pH calculation: pH = -log₁₀[H+] where [H+] is the molar concentration of hydrogen ions.
pOH calculation: pOH = -log₁₀[OH-] where [OH-] is the molar concentration of hydroxide ions.
Ion product of water: [H+] × [OH-] = 1.0 × 10⁻¹⁴ (Kw at 25°C)
pH and pOH relationship: pH + pOH = 14 (at 25°C)
Hydrogen ion concentration: [H+] = 10⁻ᵖᴴ
Hydroxide ion concentration: [OH-] = 10⁻ᵖᴼᴴ
When preparing acid or base solutions, our Dilution Calculator helps determine exact volumes for achieving target concentrations.
Common pH Values
Strong acids: Battery acid (pH 0), gastric acid (pH 1-2), lemon juice (pH 2-3), vinegar (pH 2.5)
Weak acids: Coffee (pH 5), milk (pH 6.5), pure water (pH 7.0)
Weak bases: Seawater (pH 8.0), baking soda (pH 8.5), milk of magnesia (pH 10.5)
Strong bases: Ammonia (pH 11.5), bleach (pH 12.5), sodium hydroxide (pH 13-14)
Applications of pH
pH measurement is critical in chemistry, biology, medicine, agriculture, environmental science, and industrial processes. In biological systems, pH affects enzyme activity, protein structure, and metabolic reactions. Human blood must maintain a pH between 7.35-7.45 for proper physiological function. In agriculture, soil pH determines nutrient availability for plants. Water treatment facilities monitor pH to ensure safe drinking water. Industrial processes like fermentation, pharmaceutical manufacturing, and chemical synthesis require precise pH control for optimal results. For reaction calculations involving acids and bases, try our Stoichiometry Calculator.