pH Converter

pH measures acidity or alkalinity on a scale from 0 to 14.

Core formulas:

• pH = -log₁₀[H⁺]
• pOH = -log₁₀[OH⁻]
• pH + pOH = 14 (at 25°C)
• [H⁺] = 10⁻ᵖᴴ mol/L
• [OH⁻] = 10⁻ᵖᴼᴴ mol/L
• [H⁺] × [OH⁻] = 10⁻¹⁴ (water ionization constant at 25°C)

The pH scale:

Important: Each whole pH unit represents a 10× change in H⁺ concentration. pH 3 is 10 times more acidic than pH 4. pH 3 is 100 times more acidic than pH 5.

The pH scale comes straight from chemistry: pH is the negative base-10 logarithm of the hydrogen-ion concentration. That logarithm is why the scale behaves as the page describes, with each whole step a tenfold change in acidity. It also means pH squeezes an enormous range, from strongly acidic to strongly basic, into a tidy span from 0 to 14.

That logarithmic nature has real consequences. Lowering a pool’s pH from 8 to 7 isn’t a small nudge, it’s a tenfold shift in acidity, which is why pool and aquarium guides warn against big sudden adjustments. Two subtleties are worth knowing: the 0-to-14 range is a convention rather than a hard limit, since very strong acids and bases can fall outside it, and the neutral point isn’t always exactly 7. It’s 7 for pure water at 25°C, but it shifts slightly with temperature, because the water equilibrium the scale rests on changes with heat.