pH Calculator
pH, pOH and ion concentrations.
Enter your values
Enter the value you are working with.
Choose one of: pH, pOH, [H⁺] in mol/L, [OH⁻] in mol/L.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- pH
- 3.5
- pOH
- 10.5
- [H⁺]
- 3.1623e-4 mol/L
- [OH⁻]
- 3.1623e-11 mol/L
- Classification
- Acidic
Working
- 1pH = −log₁₀(3.162e-4) = 3.5
Quick answer
pH = −log₁₀[H⁺], and pH + pOH = 14 at 25°C.
pH = −log₁₀[H⁺]
At a glance
| What it does | pH, pOH and ion concentrations. |
|---|---|
| Category | Chemistry |
| Inputs needed | Value, Given |
| Main output | pH |
| Formula | pH = −log₁₀[H⁺] |
| Cost | Free — no sign-up, no download |
How to use the pH Calculator
- 1Enter the value you know.
- 2Select which quantity it is.
- 3Read pH, pOH and both ion concentrations.
Inputs explained
- Value
- Enter the value you are working with.
- Given
- Choose one of: pH, pOH, [H⁺] in mol/L, [OH⁻] in mol/L.
Worked example
Using the values the calculator loads with:
Inputs
- Value3.5
- GivenpH
Results
- pH3.5
- pOH10.5
- [H⁺]3.1623e-4 mol/L
- [OH⁻]3.1623e-11 mol/L
- ClassificationAcidic
- pH = −log₁₀(3.162e-4) = 3.5
Frequently asked questions
Why is pH 7 neutral?
At 25°C water self-ionises so [H⁺] = [OH⁻] = 10⁻⁷ mol/L. At other temperatures neutral pH shifts slightly.
Can pH be negative?
Yes. Concentrated strong acids above 1 M give negative pH values.
What do I need to enter into the pH Calculator?
Just 2 values: value, given. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the pH Calculator work out the answer?
pH = −log₁₀[H⁺], and pH + pOH = 14 at 25°C. It applies the formula pH = −log₁₀[H⁺] and shows the working so you can check each step by hand.
Is the pH Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.