pH Calculator

pH measures how acidic or basic a solution is — a value below 7 is acidic, above 7 is basic, and 7 is neutral. The pH Calculator lets you select your calculation type — from [H⁺] or [OH⁻] concentration to strong acid, strong base, weak acid (Ka), or weak base (Kb) — then enter the relevant concentration and equilibrium constants to get your pH, pOH, both ion concentrations, and solution type. Also try the find Total Buffer Capacity (βtotal) with Buffer Capacity Calculator.

mol/L

Enter hydrogen ion concentration in mol/L

mol/L

Enter hydroxide ion concentration in mol/L

mol/L

Enter analytical concentration of acid

mol/L

Enter analytical concentration of base

Number of H⁺ or OH⁻ ions per molecule

Enter Ka value for weak acid

Enter Kb value for weak base

Results

pH

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pOH

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[H⁺] Concentration

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[OH⁻] Concentration

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Solution Type

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Frequently Asked Questions

What is pH and how is it calculated?

pH is a measure of acidity or basicity of a solution. It's calculated as pH = -log[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. The pH scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

How do I calculate pH from H⁺ concentration?

To calculate pH from hydrogen ion concentration, use the formula pH = -log[H⁺]. For example, if [H⁺] = 0.001 mol/L, then pH = -log(0.001) = 3. Simply enter your H⁺ concentration in the calculator.

What's the difference between pH and pOH?

pH measures hydrogen ion concentration while pOH measures hydroxide ion concentration. At 25°C, pH + pOH = 14. When pH is low (acidic), pOH is high, and vice versa.

How do I calculate pH for weak acids and bases?

For weak acids, you need the Ka value and concentration. The calculator solves the quadratic equation Ka = x²/(C-x) to find [H⁺]. For weak bases, it uses Kb and solves for [OH⁻], then converts to pH.

What are some common pH values?

Pure water has pH 7 (neutral). Lemon juice is around pH 2 (acidic), coffee is pH 5, baking soda is pH 9 (basic), and household ammonia is pH 11. Battery acid can be pH 0, while lye solution can be pH 14.

Can I calculate pH from mass and volume?

Yes, but you'll first need to calculate the molarity (concentration). Divide the moles of substance by the volume in liters to get mol/L, then use this concentration in the pH calculation.

Why is the pH scale logarithmic?

The pH scale is logarithmic because hydrogen ion concentrations can vary over many orders of magnitude (from 10⁻¹⁴ to 10⁰ mol/L). The logarithmic scale compresses this wide range into a manageable 0-14 scale.

What happens when I mix acids and bases?

When you mix acids and bases, they neutralize each other. The resulting pH depends on the strength and amounts of each. Strong acid + strong base gives pH 7, but weak acid/base mixtures can give different pH values depending on their relative strengths.