Science

pH Calculator

Calculate pH, pOH, and classify acid/base strength.

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pH Calculator

Input Type

Value

Results

Formula & Methodology

pH = -log₁₀[H⁺]
pOH = -log₁₀[OH⁻]
pH + pOH = 14 (at 25°C)

[H⁺] = 10^(-pH)
[OH⁻] = 10^(-pOH)

pH Scale:
0-3: Strongly Acidic
3-7: Weakly Acidic
7: Neutral
7-11: Weakly Basic
11-14: Strongly Basic

About pH Calculator

The pH scale measures how acidic or basic (alkaline) a solution is. Our calculator converts between pH values and hydrogen ion concentrations, and classifies solutions on the acid-base spectrum.

Frequently Asked Questions

pH measures the acidity or alkalinity of a solution on a scale from 0 to 14. pH 7 is neutral (pure water). Values below 7 are acidic (more H⁺ ions); values above 7 are alkaline/basic (more OH⁻ ions). The scale is logarithmic — each unit represents a 10× difference.

pH = −log₁₀[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. Conversely, [H⁺] = 10^(−pH). For example, pH 3: [H⁺] = 0.001 mol/L; pH 7: [H⁺] = 10⁻⁷ mol/L.

pH 0-1: Battery acid, HCl. pH 2-3: Lemon juice, vinegar, stomach acid. pH 4-5: Coffee, beer, tomatoes. pH 6-7: Milk, pure water, healthy skin. pH 8-9: Seawater, baking soda. pH 10-11: Milk of magnesia, ammonia. pH 12-14: Bleach, lye.

A buffer solution resists changes in pH when small amounts of acid or base are added. It contains a weak acid and its conjugate base (or vice versa). Blood pH (7.35–7.45) is maintained by the bicarbonate buffer system — vital for health.

pOH = −log₁₀[OH⁻], measuring hydroxide ion concentration. The relationship: pH + pOH = 14 (at 25°C). So pH 3 → pOH = 11; pH 11 → pOH = 3. As pH increases, pOH decreases proportionally.

pH affects: soil fertility (most plants thrive at pH 6-7), water treatment (drinking water pH 6.5-8.5), medicine (drug stability, body pH balance), food preservation (low pH inhibits bacterial growth), aquarium health, hair and skin care products, and industrial processes.

Normal blood pH is 7.35–7.45 (slightly alkaline). This narrow range is critical for enzyme function and cellular metabolism. pH below 7.35 is acidosis; above 7.45 is alkalosis. Both are medical emergencies if severe. The body tightly regulates blood pH through breathing rate and kidney function.

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