pH / pOH Calculator
pH, pOH, [H⁺], and [OH⁻] with an acidity scale
About this calculator
The pH / pOH Calculator converts between the four linked acidity measures — pH, pOH, [H⁺], and [OH⁻] — from any single one, using the 25 °C water relationships pH + pOH = 14, pH = −log₁₀[H⁺], and Kw = [H⁺][OH⁻] = 1.0×10⁻¹⁴. It classifies the solution as acidic, neutral, or basic and marks it on a pH scale. Concentrations must be positive; pH and pOH may be any real number, including values below 0 or above 14.
How to use the pH / pOH Calculator calculator
- Enter the quantities you know, using the units shown on each field.
- Read the computed results — they update instantly as you type.
- Use the visual explanation to see how the quantities relate.
- Copy the page URL to share the exact calculation.
Common examples
- pH 3 → pOH 11, [H⁺] = 0.001 mol/L, [OH⁻] = 10⁻¹¹ mol/L: acidic
- [H⁺] = 2.5×10⁻⁵ mol/L → pH ≈ 4.60, pOH ≈ 9.40: acidic
- pOH 4 → pH 10, [OH⁻] = 10⁻⁴ mol/L: basic
- [OH⁻] = 0.01 mol/L → pH 12, [H⁺] = 10⁻¹² mol/L: basic
Frequently asked questions
How does the pH / pOH Calculator calculator work?
Enter the known quantities and the calculator applies the governing physical law or scientific formula to find the unknowns, stating the equation it used and the units of every result. Computations run at high precision.
When would I use the pH / pOH Calculator calculator?
It suits physics and chemistry homework, lab work, engineering estimates, and any time you want to explore how changing one quantity affects the others in a well-defined scientific relationship.
How accurate are the results?
The formula itself is evaluated at 30 significant digits of precision. Keep in mind that idealized models — such as neglecting friction, air resistance or measurement error — bound the real-world accuracy more than the arithmetic does.
Can I share a specific calculation with someone else?
Yes. Every value you enter updates the URL, so copying the address bar and sharing the link reopens the exact same calculation for whoever clicks it.