pH Calculator
Find pH, pOH, hydrogen-ion concentration, or hydroxide-ion concentration from the values you know.
Result
pH
1.00
Acidic
- pOH
- 13.00
- [H⁺]
- 0.100 M
- [OH⁻]
- 1.00 × 10⁻¹³ M
- Percent dissociation
Water autoionization is included in this calculation.
Examples
Calculation working
Calculate the pH
1. Find hydrogen-ion concentration
[H⁺] = 0.100 M
2. Calculate pH
pH = −log₁₀(0.100)
pH = 1.00
3. Find pOH
pOH = 14.00 − 1.00
pOH = 13.00
Important concept
pH depends on hydrogen-ion concentration
pH tells you how acidic or basic an aqueous solution is based on its hydrogen-ion concentration.
pH = −log₁₀[H⁺]
Strong and weak acids are calculated differently
Strong acid
Dissociates essentially completely.
0.100 M HCl → [H⁺] ≈ 0.100 M
Weak acid
Only partially dissociates.
0.100 M acetic acid → [H⁺] is much lower than 0.100 M
The same idea applies to strong and weak bases.
Concentration alone is not enough for a weak acid or base. You also need Ka or Kb.
pH vs pOH
pH
Measures hydrogen-ion concentration.
pOH
Measures hydroxide-ion concentration.
At 25 °C: pH + pOH = 14
Scope
What this calculator handles
It handles:
- Strong acids
- Strong bases
- Weak acids
- Weak bases
- pH
- pOH
- [H⁺]
- [OH⁻]
- Ka / pKa
- Kb / pKb
- Percent dissociation
- Common concentration units
- Step-by-step working
- 25 °C water chemistry
Use another Chemistry Inspect tool for:
FAQ
Frequently asked questions
What is pH?
pH is a logarithmic measure based on the hydrogen-ion concentration of an aqueous solution. pH = −log₁₀[H⁺].
How do I calculate pH from concentration?
For a strong acid or base, the concentration can be used to determine the relevant ion concentration. For a weak acid or base, you also need Ka or Kb because the substance only partially dissociates.
What is the difference between a strong and weak acid?
A strong acid dissociates essentially completely in water. A weak acid only partially dissociates and reaches an equilibrium.
Can I calculate pH for a weak acid?
Yes. Enter its initial concentration and Ka or pKa. The calculator solves the equilibrium rather than simply treating the acid as fully dissociated.
Can I calculate pH for a weak base?
Yes. Enter its initial concentration and Kb or pKb.
What is pOH?
pOH is the logarithmic measure of hydroxide-ion concentration. pOH = −log₁₀[OH⁻]. At 25 °C, pH + pOH = 14.
Can I calculate [H⁺] from pH?
Yes. [H⁺] = 10⁻ᵖᴴ. The calculator can also work backward from [H⁺] to pH.
Can I calculate [OH⁻] from pOH?
Yes. [OH⁻] = 10⁻ᵖᴼᴴ.
Why isn't pH always between 0 and 14?
The familiar 0–14 scale is useful for many dilute aqueous solutions at 25 °C, but pH can be below 0 or above 14 for sufficiently concentrated solutions.
Does this calculator work for buffers?
No. Buffer solutions need a different calculation involving a weak acid/base and its conjugate partner. Use the future Buffer pH Calculator for that.
Does temperature affect pH?
Yes. This calculator assumes 25 °C and uses Kw = 1.00 × 10⁻¹⁴ at that temperature. Results for other temperatures can differ.