What This Tool Does
Choose pH, pOH, Hydrogen ion concentration [H+], or Hydroxide ion concentration [OH-] in Calculate from. Enter that value, then click Calculate to get the other three values, the acidic/neutral/basic classification, and the calculation steps.
The Governing Formula
The core relationships used are:
pH = -log10[H+], so[H+] = 10^-pHpOH = -log10[OH-], so[OH-] = 10^-pOHpH + pOH = 14(at 25°C)[H+][OH-] = Kw = 1.0 x 10^-14(the ion product of water at 25°C)
For a concentration input, the calculator first converts the selected unit to mol/L, then applies these relationships. The conversion is shown in Formula & steps.
Inputs & Supported Units
- pH and pOH: enter a number. Common aqueous solutions are typically between 0 and 14.
- Hydrogen ion concentration [H+] and Hydroxide ion concentration [OH-]: choose mol/L (M), mmol/L (mM), µmol/L (µM), or nmol/L (nM).
Assumptions & Limitations
The calculation assumes a dilute aqueous solution at 25°C, uses Kw = 1.0 x 10^-14, and treats pH 7 as neutral. It does not adjust for temperature, ionic strength, activity coefficients, or non-ideal solution behavior. It does not identify a specific acid or base, measure a physical sample, or provide certified laboratory or professional advice.
Input Validation
Empty input and non-numeric text are rejected. Parsed values must be finite, and the parser rejects values whose absolute magnitude exceeds 1e12. Concentration inputs must be greater than zero. Concentration calculations also reject a non-finite derived pH or pOH; the pH and pOH input paths do not use that same explicit derived-result check.
How to Use the pH Calculator
- Use Calculate from to choose pH, pOH, Hydrogen ion concentration [H+], or Hydroxide ion concentration [OH-].
- Enter the value. For a concentration, choose its Unit.
- Click Calculate, then review the four values, classification, and Formula & steps.
- Use Copy result or Download result (.txt) to save the output as plain text.
- Click Reset to clear the input, restore pH and mol/L (M), and hide the result.
Privacy & Page Scope
The calculator script performs the calculation in your browser and does not send the entered calculation value as part of the calculation. This statement applies to the calculator operation, not to other page features.
Frequently Asked Questions
What is the pH formula?
pH = -log10[H+], where [H+] is the hydrogen ion (hydronium) concentration in moles per liter. Equivalently, [H+] = 10^-pH.
How are pH and pOH related?
For a dilute aqueous solution at 25°C, pH + pOH = 14. This follows from the ion product of water, Kw = [H+][OH-] = 1.0 x 10^-14 at that temperature.
Can I enter [H+] or [OH-] instead of pH?
Yes. Choose Hydrogen ion concentration [H+] or Hydroxide ion concentration [OH-] from Calculate from, enter the value with its unit (mol/L, mmol/L, µmol/L, or nmol/L), and the calculator computes pH, pOH, and the other ion concentration.
How does the calculator decide if a solution is acidic, neutral, or basic?
A pH below 7 is classified as acidic, a pH of exactly 7 is neutral, and a pH above 7 is basic. This classification assumes a dilute aqueous solution at 25°C, where neutral pH is 7.
Does this calculator account for temperature or ionic strength?
No. It assumes a dilute aqueous solution at 25°C, where the ion product of water Kw is 1.0 x 10^-14. It performs deterministic arithmetic only and does not adjust Kw for temperature, ionic strength, or non-ideal solution behavior.