pH / Acid-Base Calculator

Because pH is a logarithmic measure, each single unit represents a tenfold change in hydrogen-ion concentration — a solution of pH 3 is not "twice as acidic" as pH 6, it's a million times more concentrated in H⁺. This is why a shift of just 0.1 pH units in ocean water, or a swing from pH 7.4 to 7.35 in human blood, represents a real and significant change in ion concentration even though the numbers look small. The scale exists because [H⁺] in everyday solutions spans more than 14 orders of magnitude — from about 10⁻¹⁴ mol/L in strong bases to 10⁰ mol/L in strong acids — and a logarithm compresses that enormous range into a single easy-to-read number from 0 to 14.

At heart, pH just reports how crowded the free hydrogen ions (H⁺) are in a water-based liquid — the more crowded, the more acidic. Pure water splits slightly into equal amounts of H⁺ and OH⁻ (about 10⁻⁷ mol/L of each at room temperature), which is why neutral lands at pH 7. Since pH + pOH always adds to 14, knowing any one of pH, pOH, [H⁺], or [OH⁻] pins down the other three — which is exactly what this tool does.

The neat rules that neutral means pH 7 and that pH + pOH = 14 hold only at 25°C. Water self-ionizes more readily when it is hot, so its ion product K_w grows with temperature: pure water is neutral at about pH 6.8 at body temperature (37°C) and near pH 6 close to boiling. The water is still perfectly neutral — equal H⁺ and OH⁻ — so the famous 7 is really just a room-temperature coincidence.