pH Calculator
Calculate the pH of a solution from its hydrogen ion concentration.
What is the pH Calculator?
The pH calculator determines the acidity or basicity of a solution from its hydrogen ion concentration [H⁺]. pH is a logarithmic scale ranging from 0 to 14 that tells you how acidic or basic a solution is. This calculator is essential for chemistry students, laboratory technicians, aquarists, gardeners, and anyone who works with aqueous solutions and needs to know their acid-base balance.
How to Use the pH Calculator
- Enter the hydrogen ion concentration [H⁺] in moles per liter
- You can use standard notation (e.g. 0.0001) or scientific notation (e.g. 1e-4)
- Press Calculate pH to see the pH, pOH, solution nature, and hydroxide concentration
pH Formula
- pH = −log₁₀[H⁺]
- pOH = 14 − pH
- [OH⁻] = 10⁻ᵖᴼᴴ
Because pH is logarithmic, each unit represents a tenfold change in hydrogen ion concentration. A solution with pH 3 is ten times more acidic than one with pH 4.
Example Calculation
| Field | Value |
|---|---|
| [H⁺] | 1.0 × 10⁻³ mol/L |
| pH | 3.00 (Acidic) |
| pOH | 11.00 |
| [OH⁻] | 1.0 × 10⁻¹¹ mol/L |
pH Scale and Classification
- Acidic: pH less than 7
- Neutral: pH equal to 7 (pure water at 25°C)
- Basic (alkaline): pH greater than 7
Common examples include lemon juice (pH ~2), coffee (pH ~5), pure water (pH 7), and baking soda solution (pH ~9).
Why Calculate pH?
pH affects nearly every chemical and biological process. Enzymes and metabolic reactions in the human body operate within narrow pH ranges, and the blood must stay near pH 7.4. In agriculture, soil pH determines nutrient availability for plants. In industry, controlling pH is critical for water treatment, food preservation, brewing, and pharmaceutical production. Knowing the pH of a solution helps you predict its chemical behavior and make informed decisions.
How the pH Calculator Works
The calculator takes your hydrogen ion concentration and computes the negative base-10 logarithm to find the pH. It then subtracts this value from 14 to obtain the pOH, uses the pOH to calculate the hydroxide ion concentration, and classifies the solution as acidic, neutral, or basic. All calculations are performed instantly and locally in your browser without transmitting your data.
Frequently Asked Questions
What is the difference between pH and pOH?
pH measures the hydrogen ion concentration while pOH measures the hydroxide ion concentration. In water at 25°C, pH + pOH always equals 14.
Why does a small pH change matter?
Because the scale is logarithmic, a change of just 1 pH unit represents a tenfold change in hydrogen ion concentration. A change of 2 units is a hundredfold change.
Can pH be negative or above 14?
Yes, in extremely concentrated acid or base solutions, pH can fall outside the 0 to 14 range, though the 0–14 range covers nearly all everyday solutions.