In a neutral solution, the concentration of hydronium ions (H₃O⁺) and hydroxide ions (OH⁻) are equal.

At 25°C, this concentration is 1.0 x 10⁻⁷ M for both ions.

This is because the product of their concentrations is always equal to the ion product constant of water (Kw), which is 1.0 x 10⁻¹⁴ at 25°C:

[H₃O⁺] * [OH⁻] = Kw = 1.0 x 10⁻¹⁴